From: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
To: Stephen Hemminger <stephen@networkplumber.org>,
"Jacob, Jerin" <Jerin.JacobKollanukkaran@cavium.com>
Cc: "bruce.richardson@intel.com" <bruce.richardson@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] eal: roundup tsc frequency when estimating it
Date: Fri, 30 Nov 2018 07:17:00 +0000 [thread overview]
Message-ID: <20181130071641.GA11625@ltp-pvn> (raw)
In-Reply-To: <20181129132152.754ce410@xeon-e3>
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.
next prev parent reply other threads:[~2018-11-30 7:17 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-29 8:32 Pavan Nikhilesh
2018-11-29 9:08 ` Jerin Jacob
2018-11-29 21:21 ` Stephen Hemminger
2018-11-30 7:17 ` Pavan Nikhilesh [this message]
2019-03-16 7:03 ` [dpdk-dev] [PATCH v2 1/2] eal: add macro to align value to the nearest multiple Pavan Nikhilesh Bhagavatula
2019-03-16 7:03 ` Pavan Nikhilesh Bhagavatula
2019-03-16 7:03 ` [dpdk-dev] [PATCH v2 2/2] eal: roundup tsc frequency when estimating it Pavan Nikhilesh Bhagavatula
2019-03-16 7:03 ` Pavan Nikhilesh Bhagavatula
2019-03-16 14:42 ` Wiles, Keith
2019-03-16 14:42 ` Wiles, Keith
2019-03-16 15:06 ` [dpdk-dev] [EXT] " Pavan Nikhilesh Bhagavatula
2019-03-16 15:06 ` Pavan Nikhilesh Bhagavatula
2019-03-16 17:18 ` Wiles, Keith
2019-03-16 17:18 ` Wiles, Keith
2019-03-16 17:56 ` Pavan Nikhilesh Bhagavatula
2019-03-16 17:56 ` Pavan Nikhilesh Bhagavatula
2019-03-16 18:22 ` Wiles, Keith
2019-03-16 18:22 ` Wiles, Keith
2019-03-16 18:27 ` Pavan Nikhilesh Bhagavatula
2019-03-16 18:27 ` Pavan Nikhilesh Bhagavatula
2019-03-16 19:01 ` [dpdk-dev] [PATCH v3 1/2] eal: add macro to align value to the nearest multiple Pavan Nikhilesh Bhagavatula
2019-03-16 19:01 ` Pavan Nikhilesh Bhagavatula
2019-03-16 19:01 ` [dpdk-dev] [PATCH v3 2/2] eal: roundup tsc frequency when estimating Pavan Nikhilesh Bhagavatula
2019-03-16 19:01 ` Pavan Nikhilesh Bhagavatula
2019-03-27 22:43 ` Thomas Monjalon
2019-03-27 22:43 ` Thomas Monjalon
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