diff mbox series

[v4] kni: allow configuring the kni thread granularity

Message ID 1637781854-74761-1-git-send-email-tudor.cornea@gmail.com (mailing list archive)
State Superseded, archived
Delegated to: Thomas Monjalon
Headers show
Series [v4] kni: allow configuring the kni thread granularity | expand

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ci/iol-intel-Functional success Functional Testing PASS
ci/checkpatch success coding style OK

Commit Message

Tudor Cornea Nov. 24, 2021, 7:24 p.m. UTC
The Kni kthreads seem to be re-scheduled at a granularity of roughly
1 millisecond right now, which seems to be insufficient for performing
tests involving a lot of control plane traffic.

Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
seems that the existing code cannot reschedule at the desired granularily,
due to precision constraints of schedule_timeout_interruptible().

In our use case, we leverage the Linux Kernel for control plane, and
it is not uncommon to have 60K - 100K pps for some signaling protocols.

Since we are not in atomic context, the usleep_range() function seems to be
more appropriate for being able to introduce smaller controlled delays,
in the range of 5-10 microseconds. Upon reading the existing code, it would
seem that this was the original intent. Adding sub-millisecond delays,
seems unfeasible with a call to schedule_timeout_interruptible().

KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
schedule_timeout_interruptible(
        usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));

Below, we attempted a brief comparison between the existing implementation,
which uses schedule_timeout_interruptible() and usleep_range().

We attempt to measure the CPU usage, and RTT between two Kni interfaces,
which are created on top of vmxnet3 adapters, connected by a vSwitch.

insmod rte_kni.ko kthread_mode=single carrier=on

schedule_timeout_interruptible(usecs_to_jiffies(5))
kni_single CPU Usage: 2-4 %
[root@localhost ~]# ping 1.1.1.2 -I eth1
PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms

usleep_range(5, 10)
kni_single CPU usage: 50%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms

usleep_range(20, 50)
kni_single CPU usage: 24%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms

usleep_range(50, 100)
kni_single CPU usage: 13%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms

usleep_range(100, 200)
kni_single CPU usage: 7%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms

usleep_range(1000, 1100)
kni_single CPU usage: 2%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms

Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
latency and cpu usage to the variant with schedule_timeout_interruptible(),
while usleep_range(100, 200) seems to give a decent tradeoff between
latency and cpu usage, while allowing users to tweak the limits for
improved precision if they have such use cases.

Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
softlockup on my kernel.

Kernel panic - not syncing: softlockup: hung tasks
CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
 <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
 [<ffffffff814f7891>] panic+0xcd/0x1e0
 [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
 [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
 [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
 [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
 [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80

This patch also attempts to remove this option.

References:
[1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>

---
v4:
* Removed RTE_KNI_PREEMPT_DEFAULT configuration option
v3:
* Fixed unwrapped commit description warning
* Changed from hrtimers to Linux High Precision Timers in docs
* Added two tabs at the beginning of the new params description.
  Stephen correctly pointed out that the descriptions of the parameters
  for the Kni module are nonstandard w.r.t existing kernel code.
  I was thinking to preserve compatibility with the existing parameters
  of the Kni module for the moment, while an additional clean-up patch
  could format the descriptions to be closer to the kernel standard.
v2:
* Fixed some spelling errors
---
 config/rte_config.h                            |  3 ---
 doc/guides/prog_guide/kernel_nic_interface.rst | 33 +++++++++++++++++++++++++
 kernel/linux/kni/kni_dev.h                     |  2 +-
 kernel/linux/kni/kni_misc.c                    | 34 ++++++++++++++++++++------
 4 files changed, 60 insertions(+), 12 deletions(-)

Comments

Connolly, Padraig J Jan. 14, 2022, 1:53 p.m. UTC | #1
> -----Original Message-----
> From: Tudor Cornea <tudor.cornea@gmail.com>
> Sent: Wednesday, November 24, 2021 7:24 PM
> To: Yigit, Ferruh <ferruh.yigit@intel.com>
> Cc: thomas@monjalon.net; stephen@networkplumber.org; Zhang, Helin
> <helin.zhang@intel.com>; dev@dpdk.org; Tudor Cornea
> <tudor.cornea@gmail.com>
> Subject: [PATCH v4] kni: allow configuring the kni thread granularity
> 
> The Kni kthreads seem to be re-scheduled at a granularity of roughly
> 1 millisecond right now, which seems to be insufficient for performing tests
> involving a lot of control plane traffic.
> 
> Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
> seems that the existing code cannot reschedule at the desired granularily,
> due to precision constraints of schedule_timeout_interruptible().
> 
> In our use case, we leverage the Linux Kernel for control plane, and it is not
> uncommon to have 60K - 100K pps for some signaling protocols.
> 
> Since we are not in atomic context, the usleep_range() function seems to be
> more appropriate for being able to introduce smaller controlled delays, in the
> range of 5-10 microseconds. Upon reading the existing code, it would seem
> that this was the original intent. Adding sub-millisecond delays, seems
> unfeasible with a call to schedule_timeout_interruptible().
> 
> KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
> schedule_timeout_interruptible(
>         usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> 
> Below, we attempted a brief comparison between the existing
> implementation, which uses schedule_timeout_interruptible() and
> usleep_range().
> 
> We attempt to measure the CPU usage, and RTT between two Kni interfaces,
> which are created on top of vmxnet3 adapters, connected by a vSwitch.
> 
> insmod rte_kni.ko kthread_mode=single carrier=on
> 
> schedule_timeout_interruptible(usecs_to_jiffies(5))
> kni_single CPU Usage: 2-4 %
> [root@localhost ~]# ping 1.1.1.2 -I eth1 PING 1.1.1.2 (1.1.1.2) from 1.1.1.1
> eth1: 56(84) bytes of data.
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms
> 
> usleep_range(5, 10)
> kni_single CPU usage: 50%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms
> 
> usleep_range(20, 50)
> kni_single CPU usage: 24%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms
> 
> usleep_range(50, 100)
> kni_single CPU usage: 13%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms
> 
> usleep_range(100, 200)
> kni_single CPU usage: 7%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms
> 
> usleep_range(1000, 1100)
> kni_single CPU usage: 2%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms
> 
> Upon testing, usleep_range(1000, 1100) seems roughly equivalent in latency
> and cpu usage to the variant with schedule_timeout_interruptible(), while
> usleep_range(100, 200) seems to give a decent tradeoff between latency
> and cpu usage, while allowing users to tweak the limits for improved
> precision if they have such use cases.
> 
> Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
> softlockup on my kernel.
> 
> Kernel panic - not syncing: softlockup: hung tasks
> CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
>  <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b  [<ffffffff814f7891>]
> panic+0xcd/0x1e0  [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
> [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0  [<ffffffff81064b57>]
> hrtimer_interrupt+0xe7/0x1f0  [<ffffffff8102cd57>]
> smp_apic_timer_interrupt+0x67/0xa0
>  [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80
> 
> This patch also attempts to remove this option.
> 
> References:
> [1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt
> 
> Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
> 
> ---
> v4:
> * Removed RTE_KNI_PREEMPT_DEFAULT configuration option
> v3:
> * Fixed unwrapped commit description warning
> * Changed from hrtimers to Linux High Precision Timers in docs
> * Added two tabs at the beginning of the new params description.
>   Stephen correctly pointed out that the descriptions of the parameters
>   for the Kni module are nonstandard w.r.t existing kernel code.
>   I was thinking to preserve compatibility with the existing parameters
>   of the Kni module for the moment, while an additional clean-up patch
>   could format the descriptions to be closer to the kernel standard.
> v2:
> * Fixed some spelling errors
> ---
>  config/rte_config.h                            |  3 ---
>  doc/guides/prog_guide/kernel_nic_interface.rst | 33
> +++++++++++++++++++++++++
>  kernel/linux/kni/kni_dev.h                     |  2 +-
>  kernel/linux/kni/kni_misc.c                    | 34 ++++++++++++++++++++------
>  4 files changed, 60 insertions(+), 12 deletions(-)
> 
> diff --git a/config/rte_config.h b/config/rte_config.h index cab4390..91d96ee
> 100644
> --- a/config/rte_config.h
> +++ b/config/rte_config.h
> @@ -95,9 +95,6 @@
>  #define RTE_SCHED_PORT_N_GRINDERS 8
>  #undef RTE_SCHED_VECTOR
> 
> -/* KNI defines */
> -#define RTE_KNI_PREEMPT_DEFAULT 1
> -
>  /* rte_graph defines */
>  #define RTE_GRAPH_BURST_SIZE 256
>  #define RTE_LIBRTE_GRAPH_STATS 1
> diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst
> b/doc/guides/prog_guide/kernel_nic_interface.rst
> index 1ce03ec..fce3667 100644
> --- a/doc/guides/prog_guide/kernel_nic_interface.rst
> +++ b/doc/guides/prog_guide/kernel_nic_interface.rst
> @@ -56,6 +56,10 @@ can be specified when the module is loaded to control
> its behavior:
>                      off   Interfaces will be created with carrier state set to off.
>                      on    Interfaces will be created with carrier state set to on.
>                       (charp)
> +    parm:           min_scheduling_interval: "Kni thread min scheduling interval
> (default=100 microseconds):
> +                     (long)
> +    parm:           max_scheduling_interval: "Kni thread max scheduling interval
> (default=200 microseconds):
> +                     (long)
> 
>  Loading the ``rte_kni`` kernel module without any optional parameters is
> the typical way a DPDK application gets packets into and out of the kernel
> @@ -174,6 +178,35 @@ To set the default carrier state to *off*:
>  If the ``carrier`` parameter is not specified, the default carrier state  of KNI
> interfaces will be set to *off*.
> 
> +KNI Kthread Scheduling
> +~~~~~~~~~~~~~~~~~~~~~~
> +
> +The ``min_scheduling_interval`` and ``max_scheduling_interval``
> +parameters control the rescheduling interval of the KNI kthreads.
> +
> +This might be useful if we have use cases in which we require improved
> +latency or performance for control plane traffic.
> +
> +The implementation is backed by Linux High Precision Timers, and uses
> ``usleep_range``.
> +Hence, it will have the same granularity constraints as this Linux subsystem.
> +
> +For Linux High Precision Timers, you can check the following resource:
> +`Kernel Timers
> +<http://www.kernel.org/doc/Documentation/timers/timers-howto.txt>`_
> +
> +To set the ``min_scheduling_interval`` to a value of 100 microseconds:
> +
> +.. code-block:: console
> +
> +    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko
> + min_scheduling_interval=100
> +
> +To set the ``max_scheduling_interval`` to a value of 200 microseconds:
> +
> +.. code-block:: console
> +
> +    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko
> + max_scheduling_interval=200
> +
> +If the ``min_scheduling_interval`` and ``max_scheduling_interval``
> +parameters are not specified, the default interval limits will be set to *100*
> and *200* respectively.
> +
>  KNI Creation and Deletion
>  -------------------------
> 
> diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h index
> c15da311..bb4d891 100644
> --- a/kernel/linux/kni/kni_dev.h
> +++ b/kernel/linux/kni/kni_dev.h
> @@ -27,7 +27,7 @@
>  #include <linux/list.h>
> 
>  #include <rte_kni_common.h>
> -#define KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
> +#define KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL 1000000 /* us */
> 
>  #define MBUF_BURST_SZ 32
> 
> diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c index
> f4944e1..23132bb 100644
> --- a/kernel/linux/kni/kni_misc.c
> +++ b/kernel/linux/kni/kni_misc.c
> @@ -41,6 +41,10 @@ static uint32_t multiple_kthread_on;  static char
> *carrier;  uint32_t kni_dflt_carrier;
> 
> +/* Kni thread scheduling interval */
> +static long min_scheduling_interval = 100; /* us */ static long
> +max_scheduling_interval = 200; /* us */
> +
>  #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
> 
>  static int kni_net_id;
> @@ -128,11 +132,8 @@ kni_thread_single(void *data)
>  			}
>  		}
>  		up_read(&knet->kni_list_lock);
> -#ifdef RTE_KNI_PREEMPT_DEFAULT
>  		/* reschedule out for a while */
> -		schedule_timeout_interruptible(
> -
> 	usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> -#endif
> +		usleep_range(min_scheduling_interval,
> max_scheduling_interval);
>  	}
> 
>  	return 0;
> @@ -149,10 +150,7 @@ kni_thread_multiple(void *param)
>  			kni_net_rx(dev);
>  			kni_net_poll_resp(dev);
>  		}
> -#ifdef RTE_KNI_PREEMPT_DEFAULT
> -		schedule_timeout_interruptible(
> -
> 	usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> -#endif
> +		usleep_range(min_scheduling_interval,
> max_scheduling_interval);
>  	}
> 
>  	return 0;
> @@ -590,6 +588,14 @@ kni_init(void)
>  	else
>  		pr_debug("Default carrier state set to on.\n");
> 
> +	if (min_scheduling_interval < 0 || max_scheduling_interval < 0 ||
> +		min_scheduling_interval >
> KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
> +		max_scheduling_interval >
> KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
> +		min_scheduling_interval >= max_scheduling_interval) {
> +		pr_err("Invalid parameters for scheduling interval\n");
> +		return -EINVAL;
> +	}
> +
>  #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
>  	rc = register_pernet_subsys(&kni_net_ops);
>  #else
> @@ -656,3 +662,15 @@ MODULE_PARM_DESC(carrier,
>  "\t\ton    Interfaces will be created with carrier state set to on.\n"
>  "\t\t"
>  );
> +
> +module_param(min_scheduling_interval, long, 0644);
> +MODULE_PARM_DESC(min_scheduling_interval,
> +"\t\tKni thread min scheduling interval (default=100 microseconds):\n"
> +"\t\t"
> +);
> +
> +module_param(max_scheduling_interval, long, 0644);
> +MODULE_PARM_DESC(max_scheduling_interval,
> +"\t\tKni thread max scheduling interval (default=200 microseconds):\n"
> +"\t\t"
> +);
This patch looks good to me.

Tested with <build_dir>/kernel/linux/kni/rte_kni.ko min_scheduling_interval=20 max_scheduling_interval=50

Results:
KNI Perf before patch was added:
64 bytes from 5.5.5.6: icmp_seq=1 ttl=64 time=4.79 ms
64 bytes from 5.5.5.6: icmp_seq=2 ttl=64 time=2.97 ms
64 bytes from 5.5.5.6: icmp_seq=3 ttl=64 time=1.90 ms
64 bytes from 5.5.5.6: icmp_seq=4 ttl=64 time=7.94 ms
64 bytes from 5.5.5.6: icmp_seq=5 ttl=64 time=6.85 ms
KNI Perf after patch was added (min_scheduling_interval=20 max_scheduling_interval=50):
64 bytes from 5.5.5.6: icmp_seq=1 ttl=64 time=0.106 ms
64 bytes from 5.5.5.6: icmp_seq=2 ttl=64 time=0.055 ms
64 bytes from 5.5.5.6: icmp_seq=3 ttl=64 time=0.059 ms
64 bytes from 5.5.5.6: icmp_seq=4 ttl=64 time=0.056 ms
64 bytes from 5.5.5.6: icmp_seq=5 ttl=64 time=0.061 ms

Acked-by: Padraig Connolly <Padraig.J.Connolly@intel.com>
> --
> 2.7.4

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Ferruh Yigit Jan. 14, 2022, 2:13 p.m. UTC | #2
On 11/24/2021 7:24 PM, Tudor Cornea wrote:
> The Kni kthreads seem to be re-scheduled at a granularity of roughly
> 1 millisecond right now, which seems to be insufficient for performing
> tests involving a lot of control plane traffic.
> 
> Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
> seems that the existing code cannot reschedule at the desired granularily,
> due to precision constraints of schedule_timeout_interruptible().
> 
> In our use case, we leverage the Linux Kernel for control plane, and
> it is not uncommon to have 60K - 100K pps for some signaling protocols.
> 
> Since we are not in atomic context, the usleep_range() function seems to be
> more appropriate for being able to introduce smaller controlled delays,
> in the range of 5-10 microseconds. Upon reading the existing code, it would
> seem that this was the original intent. Adding sub-millisecond delays,
> seems unfeasible with a call to schedule_timeout_interruptible().
> 
> KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
> schedule_timeout_interruptible(
>          usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> 
> Below, we attempted a brief comparison between the existing implementation,
> which uses schedule_timeout_interruptible() and usleep_range().
> 
> We attempt to measure the CPU usage, and RTT between two Kni interfaces,
> which are created on top of vmxnet3 adapters, connected by a vSwitch.
> 
> insmod rte_kni.ko kthread_mode=single carrier=on
> 
> schedule_timeout_interruptible(usecs_to_jiffies(5))
> kni_single CPU Usage: 2-4 %
> [root@localhost ~]# ping 1.1.1.2 -I eth1
> PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms
> 
> usleep_range(5, 10)
> kni_single CPU usage: 50%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms
> 
> usleep_range(20, 50)
> kni_single CPU usage: 24%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms
> 
> usleep_range(50, 100)
> kni_single CPU usage: 13%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms
> 
> usleep_range(100, 200)
> kni_single CPU usage: 7%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms
> 
> usleep_range(1000, 1100)
> kni_single CPU usage: 2%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms
> 
> Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
> latency and cpu usage to the variant with schedule_timeout_interruptible(),
> while usleep_range(100, 200) seems to give a decent tradeoff between
> latency and cpu usage, while allowing users to tweak the limits for
> improved precision if they have such use cases.
> 
> Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
> softlockup on my kernel.
> 
> Kernel panic - not syncing: softlockup: hung tasks
> CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
>   <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
>   [<ffffffff814f7891>] panic+0xcd/0x1e0
>   [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
>   [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
>   [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
>   [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
>   [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80
> 
> This patch also attempts to remove this option.
> 
> References:
> [1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt
> 
> Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
> 
> ---
> v4:
> * Removed RTE_KNI_PREEMPT_DEFAULT configuration option
> v3:
> * Fixed unwrapped commit description warning
> * Changed from hrtimers to Linux High Precision Timers in docs
> * Added two tabs at the beginning of the new params description.
>    Stephen correctly pointed out that the descriptions of the parameters
>    for the Kni module are nonstandard w.r.t existing kernel code.
>    I was thinking to preserve compatibility with the existing parameters
>    of the Kni module for the moment, while an additional clean-up patch
>    could format the descriptions to be closer to the kernel standard.
> v2:
> * Fixed some spelling errors

Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>

Only it doesn't apply cleanly because of the latest changes in the kni,
can you please rebase it?

Please keep the review tag in the new version after rebase.
diff mbox series

Patch

diff --git a/config/rte_config.h b/config/rte_config.h
index cab4390..91d96ee 100644
--- a/config/rte_config.h
+++ b/config/rte_config.h
@@ -95,9 +95,6 @@ 
 #define RTE_SCHED_PORT_N_GRINDERS 8
 #undef RTE_SCHED_VECTOR
 
-/* KNI defines */
-#define RTE_KNI_PREEMPT_DEFAULT 1
-
 /* rte_graph defines */
 #define RTE_GRAPH_BURST_SIZE 256
 #define RTE_LIBRTE_GRAPH_STATS 1
diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst b/doc/guides/prog_guide/kernel_nic_interface.rst
index 1ce03ec..fce3667 100644
--- a/doc/guides/prog_guide/kernel_nic_interface.rst
+++ b/doc/guides/prog_guide/kernel_nic_interface.rst
@@ -56,6 +56,10 @@  can be specified when the module is loaded to control its behavior:
                     off   Interfaces will be created with carrier state set to off.
                     on    Interfaces will be created with carrier state set to on.
                      (charp)
+    parm:           min_scheduling_interval: "Kni thread min scheduling interval (default=100 microseconds):
+                     (long)
+    parm:           max_scheduling_interval: "Kni thread max scheduling interval (default=200 microseconds):
+                     (long)
 
 Loading the ``rte_kni`` kernel module without any optional parameters is
 the typical way a DPDK application gets packets into and out of the kernel
@@ -174,6 +178,35 @@  To set the default carrier state to *off*:
 If the ``carrier`` parameter is not specified, the default carrier state
 of KNI interfaces will be set to *off*.
 
+KNI Kthread Scheduling
+~~~~~~~~~~~~~~~~~~~~~~
+
+The ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters
+control the rescheduling interval of the KNI kthreads.
+
+This might be useful if we have use cases in which we require improved
+latency or performance for control plane traffic.
+
+The implementation is backed by Linux High Precision Timers, and uses ``usleep_range``.
+Hence, it will have the same granularity constraints as this Linux subsystem.
+
+For Linux High Precision Timers, you can check the following resource: `Kernel Timers <http://www.kernel.org/doc/Documentation/timers/timers-howto.txt>`_
+
+To set the ``min_scheduling_interval`` to a value of 100 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko min_scheduling_interval=100
+
+To set the ``max_scheduling_interval`` to a value of 200 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko max_scheduling_interval=200
+
+If the ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters are
+not specified, the default interval limits will be set to *100* and *200* respectively.
+
 KNI Creation and Deletion
 -------------------------
 
diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h
index c15da311..bb4d891 100644
--- a/kernel/linux/kni/kni_dev.h
+++ b/kernel/linux/kni/kni_dev.h
@@ -27,7 +27,7 @@ 
 #include <linux/list.h>
 
 #include <rte_kni_common.h>
-#define KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
+#define KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL 1000000 /* us */
 
 #define MBUF_BURST_SZ 32
 
diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c
index f4944e1..23132bb 100644
--- a/kernel/linux/kni/kni_misc.c
+++ b/kernel/linux/kni/kni_misc.c
@@ -41,6 +41,10 @@  static uint32_t multiple_kthread_on;
 static char *carrier;
 uint32_t kni_dflt_carrier;
 
+/* Kni thread scheduling interval */
+static long min_scheduling_interval = 100; /* us */
+static long max_scheduling_interval = 200; /* us */
+
 #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
 
 static int kni_net_id;
@@ -128,11 +132,8 @@  kni_thread_single(void *data)
 			}
 		}
 		up_read(&knet->kni_list_lock);
-#ifdef RTE_KNI_PREEMPT_DEFAULT
 		/* reschedule out for a while */
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
-#endif
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 	}
 
 	return 0;
@@ -149,10 +150,7 @@  kni_thread_multiple(void *param)
 			kni_net_rx(dev);
 			kni_net_poll_resp(dev);
 		}
-#ifdef RTE_KNI_PREEMPT_DEFAULT
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
-#endif
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 	}
 
 	return 0;
@@ -590,6 +588,14 @@  kni_init(void)
 	else
 		pr_debug("Default carrier state set to on.\n");
 
+	if (min_scheduling_interval < 0 || max_scheduling_interval < 0 ||
+		min_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		max_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		min_scheduling_interval >= max_scheduling_interval) {
+		pr_err("Invalid parameters for scheduling interval\n");
+		return -EINVAL;
+	}
+
 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 	rc = register_pernet_subsys(&kni_net_ops);
 #else
@@ -656,3 +662,15 @@  MODULE_PARM_DESC(carrier,
 "\t\ton    Interfaces will be created with carrier state set to on.\n"
 "\t\t"
 );
+
+module_param(min_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(min_scheduling_interval,
+"\t\tKni thread min scheduling interval (default=100 microseconds):\n"
+"\t\t"
+);
+
+module_param(max_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(max_scheduling_interval,
+"\t\tKni thread max scheduling interval (default=200 microseconds):\n"
+"\t\t"
+);