eal: roundup tsc frequency when estimating it
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Commit Message
When estimating tsc frequency using sleep/gettime round it up to the
nearest multiple of 10Mhz for more accuracy.
Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
---
lib/librte_eal/common/eal_common_timer.c | 4 ++--
lib/librte_eal/common/include/rte_common.h | 10 ++++++++++
lib/librte_eal/linuxapp/eal/eal_timer.c | 2 +-
3 files changed, 13 insertions(+), 3 deletions(-)
Comments
-----Original Message-----
> Date: Thu, 29 Nov 2018 14:02:03 +0530
> From: "Bhagavatula, Pavan" <Pavan.Bhagavatula@cavium.com>
> To: "Jacob, Jerin" <Jerin.JacobKollanukkaran@cavium.com>
> CC: "dev@dpdk.org" <dev@dpdk.org>, "Bhagavatula, Pavan"
> <Pavan.Bhagavatula@cavium.com>
> Subject: [dpdk-dev] [PATCH] eal: roundup tsc frequency when estimating it
>
> When estimating tsc frequency using sleep/gettime round it up to the
> nearest multiple of 10Mhz for more accuracy.
>
> Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
> ---
> lib/librte_eal/common/eal_common_timer.c | 4 ++--
> lib/librte_eal/common/include/rte_common.h | 10 ++++++++++
> lib/librte_eal/linuxapp/eal/eal_timer.c | 2 +-
> 3 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/lib/librte_eal/common/eal_common_timer.c b/lib/librte_eal/common/eal_common_timer.c
> index dcf26bfea..1358bbed0 100644
> --- a/lib/librte_eal/common/eal_common_timer.c
> +++ b/lib/librte_eal/common/eal_common_timer.c
> @@ -69,7 +69,7 @@ estimate_tsc_freq(void)
> /* assume that the sleep(1) will sleep for 1 second */
> uint64_t start = rte_rdtsc();
> sleep(1);
> - return rte_rdtsc() - start;
> + return RTE_ALIGN_MUL_NEAR(rte_rdtsc() - start, 1E7);
> }
>
> void
> @@ -83,7 +83,7 @@ set_tsc_freq(void)
> if (!freq)
> freq = estimate_tsc_freq();
>
> - RTE_LOG(DEBUG, EAL, "TSC frequency is ~%" PRIu64 " KHz\n", freq / 1000);
> + RTE_LOG(INFO, EAL, "TSC frequency is ~%" PRIu64 " Hz\n", freq);
> eal_tsc_resolution_hz = freq;
> }
>
> diff --git a/lib/librte_eal/common/include/rte_common.h b/lib/librte_eal/common/include/rte_common.h
> index 66cdf60b2..e374b16b1 100644
> --- a/lib/librte_eal/common/include/rte_common.h
> +++ b/lib/librte_eal/common/include/rte_common.h
> @@ -248,6 +248,16 @@ static void __attribute__((destructor(RTE_PRIO(prio)), used)) func(void)
> #define RTE_ALIGN_MUL_FLOOR(v, mul) \
> ((v / ((typeof(v))(mul))) * (typeof(v))(mul))
>
> +/**
> + * Macro to align a value to the nearest multiple of given value.
> + */
> +#define RTE_ALIGN_MUL_NEAR(v, mul) \
> + ({ \
> + typeof(v) ceil = RTE_ALIGN_MUL_CEIL(v, mul); \
> + typeof(v) floor = RTE_ALIGN_MUL_FLOOR(v, mul); \
> + (ceil - v) > (v - floor) ? floor: ceil; \
> + })
> +
Probably it is better to have two patches.
First patch to add new API along with unit testcase.
Second patch to roundup tsc frequency when estimating it.
> /**
> * Checks if a pointer is aligned to a given power-of-two value
> *
> diff --git a/lib/librte_eal/linuxapp/eal/eal_timer.c b/lib/librte_eal/linuxapp/eal/eal_timer.c
> index bc8f05199..864d6ef29 100644
> --- a/lib/librte_eal/linuxapp/eal/eal_timer.c
> +++ b/lib/librte_eal/linuxapp/eal/eal_timer.c
> @@ -248,7 +248,7 @@ get_tsc_freq(void)
>
> double secs = (double)ns/NS_PER_SEC;
> tsc_hz = (uint64_t)((end - start)/secs);
> - return tsc_hz;
> + return RTE_ALIGN_MUL_NEAR(tsc_hz, 1E7);
> }
> #endif
> return 0;
> --
> 2.19.2
>
On Thu, 29 Nov 2018 08:32:03 +0000
Pavan Nikhilesh <pbhagavatula@caviumnetworks.com> wrote:
> When estimating tsc frequency using sleep/gettime round it up to the
> nearest multiple of 10Mhz for more accuracy.
>
> Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
Rounding reduces accuracy.
Why is this code being used? Shouldn't get_tsc_freq_arch return a
correct value?
How well does the rdmsr() logic work in VM?
It looks like Hyper-V has special MSR's for TSC frequency determination.
Hi Stephen,
On Thu, Nov 29, 2018 at 01:21:52PM -0800, Stephen Hemminger wrote:
> On Thu, 29 Nov 2018 08:32:03 +0000
> Pavan Nikhilesh <pbhagavatula@caviumnetworks.com> wrote:
>
> > When estimating tsc frequency using sleep/gettime round it up to the
> > nearest multiple of 10Mhz for more accuracy.
> >
> > Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
>
> Rounding reduces accuracy.
>
> Why is this code being used? Shouldn't get_tsc_freq_arch return a
> correct value?
This patch doesn't modify get_tsc_freq_arch(), it basically gives a more
accurate freq reading when we rely on sleep(1) i.e. only when
get_tsc_freq_arch() returns 0.
example:
static uint64_t
estimate_tsc_freq(void)
{
RTE_LOG(WARNING, EAL, "WARNING: TSC frequency estimated roughly"
" - clock timings may be less accurate.\n");
/* assume that the sleep(1) will sleep for 1 second */
uint64_t start = rte_rdtsc();
sleep(1);
return rte_rdtsc() - start;
}
This will not give the accurate cyc/sec in most cases, rounding it to 10Mhz wil
do the job.
In case of ARM64 if we enable RTE_ARM_EAL_RDTSC_USE_PMU, get_tsc_freq_arch()
will return 0 as there is no instruction to determine the clk of PMU.
>
> How well does the rdmsr() logic work in VM?
> It looks like Hyper-V has special MSR's for TSC frequency determination.
Maybe bruce can give a more accurate answer to this as it is x86 specific.
Thanks,
Pavan.
@@ -69,7 +69,7 @@ estimate_tsc_freq(void)
/* assume that the sleep(1) will sleep for 1 second */
uint64_t start = rte_rdtsc();
sleep(1);
- return rte_rdtsc() - start;
+ return RTE_ALIGN_MUL_NEAR(rte_rdtsc() - start, 1E7);
}
void
@@ -83,7 +83,7 @@ set_tsc_freq(void)
if (!freq)
freq = estimate_tsc_freq();
- RTE_LOG(DEBUG, EAL, "TSC frequency is ~%" PRIu64 " KHz\n", freq / 1000);
+ RTE_LOG(INFO, EAL, "TSC frequency is ~%" PRIu64 " Hz\n", freq);
eal_tsc_resolution_hz = freq;
}
@@ -248,6 +248,16 @@ static void __attribute__((destructor(RTE_PRIO(prio)), used)) func(void)
#define RTE_ALIGN_MUL_FLOOR(v, mul) \
((v / ((typeof(v))(mul))) * (typeof(v))(mul))
+/**
+ * Macro to align a value to the nearest multiple of given value.
+ */
+#define RTE_ALIGN_MUL_NEAR(v, mul) \
+ ({ \
+ typeof(v) ceil = RTE_ALIGN_MUL_CEIL(v, mul); \
+ typeof(v) floor = RTE_ALIGN_MUL_FLOOR(v, mul); \
+ (ceil - v) > (v - floor) ? floor: ceil; \
+ })
+
/**
* Checks if a pointer is aligned to a given power-of-two value
*
@@ -248,7 +248,7 @@ get_tsc_freq(void)
double secs = (double)ns/NS_PER_SEC;
tsc_hz = (uint64_t)((end - start)/secs);
- return tsc_hz;
+ return RTE_ALIGN_MUL_NEAR(tsc_hz, 1E7);
}
#endif
return 0;