| Message ID | 1642173499-59396-1-git-send-email-tudor.cornea@gmail.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Delegated to: | Thomas Monjalon |
| Headers | show |
| Series | [v5] kni: allow configuring the kni thread granularity | expand |
| Context | Check | Description |
|---|---|---|
| ci/iol-abi-testing | success | Testing PASS |
| ci/iol-aarch64-compile-testing | success | Testing PASS |
| ci/iol-x86_64-compile-testing | success | Testing PASS |
| ci/iol-aarch64-unit-testing | success | Testing PASS |
| ci/iol-x86_64-unit-testing | success | Testing PASS |
| ci/iol-intel-Functional | success | Functional Testing PASS |
| ci/iol-intel-Performance | success | Performance Testing PASS |
| ci/iol-broadcom-Functional | success | Functional Testing PASS |
| ci/iol-broadcom-Performance | success | Performance Testing PASS |
| ci/iol-mellanox-Performance | success | Performance Testing PASS |
| ci/github-robot: build | success | github build: passed |
| ci/checkpatch | success | coding style OK |
On Fri, 14 Jan 2022 17:18:19 +0200 Tudor Cornea <tudor.cornea@gmail.com> wrote: > +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" > +); Please don't add more bad module parameter strings. The KNI author did something no other kernel modules do with tabs and double spacing, stop this bogus stuff. Is there any reason you have to use KNI at all. KNI is broken on many levels and is not fixable. What about virtio or tap?
On 1/14/2022 4:24 PM, Stephen Hemminger wrote: > On Fri, 14 Jan 2022 17:18:19 +0200 > Tudor Cornea <tudor.cornea@gmail.com> wrote: > >> +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" >> +); > > Please don't add more bad module parameter strings. > The KNI author did something no other kernel modules do with tabs > and double spacing, stop this bogus stuff. > The patch is good, let's not block it for the module parameter string, all can be fixed with another patch. Can you please give a sample what is a common way of it, me or Tudor can do the patch? > Is there any reason you have to use KNI at all. > KNI is broken on many levels and is not fixable. > What about virtio or tap?
On Fri, 14 Jan 2022 at 18:44, Ferruh Yigit <ferruh.yigit@intel.com> wrote: > On 1/14/2022 4:24 PM, Stephen Hemminger wrote: > > On Fri, 14 Jan 2022 17:18:19 +0200 > > Tudor Cornea <tudor.cornea@gmail.com> wrote: > > > >> +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" > >> +); > > > > Please don't add more bad module parameter strings. > > The KNI author did something no other kernel modules do with tabs > > and double spacing, stop this bogus stuff. > > > > The patch is good, let's not block it for the module parameter string, > all can be fixed with another patch. > > Can you please give a sample what is a common way of it, me or Tudor can > do the patch? > > I agree that the module parameter string is in non-standard format. I was planning to send a follow-up patch, which would correct the description for all of the KNI parameters (including the two new parameters that the current patch would add) in one shot. > > Is there any reason you have to use KNI at all. > > KNI is broken on many levels and is not fixable. > > What about virtio or tap? > > We've run some tests with tap interfaces and found the performance to not be good enough for our use. We're going to experiment with virtio_user in the future. I'm aware that there is a long term plan to deprecate the KNI.
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 771c7d7..a0763c5 100644 --- a/doc/guides/prog_guide/kernel_nic_interface.rst +++ b/doc/guides/prog_guide/kernel_nic_interface.rst @@ -61,6 +61,10 @@ can be specified when the module is loaded to control its behavior: userspace callback and supporting async requests (default=off): on Enable request processing support for bifurcated drivers. (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 @@ -202,6 +206,35 @@ Enabling bifurcated device support releases ``rtnl`` lock before calling callback and locks it back after callback. Also enables asynchronous request to support callbacks that requires rtnl lock to work (interface down). +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 e863348..a2c6d9f 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 f10dcd0..c5218d5 100644 --- a/kernel/linux/kni/kni_misc.c +++ b/kernel/linux/kni/kni_misc.c @@ -45,6 +45,10 @@ uint32_t kni_dflt_carrier; static char *enable_bifurcated; uint32_t bifurcated_support; +/* 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; @@ -132,11 +136,8 @@ 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; @@ -153,10 +154,7 @@ 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; @@ -617,6 +615,14 @@ kni_init(void) if (bifurcated_support == 1) pr_debug("bifurcated support is enabled.\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 @@ -692,3 +698,15 @@ MODULE_PARM_DESC(enable_bifurcated, "\t\ton Enable request processing support for bifurcated drivers.\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" +);
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> Acked-by: Padraig Connolly <Padraig.J.Connolly@intel.com> Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com> --- v5: * Rebased the patch on top of the dpdk-next-net branch 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(-)