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From: bugzilla@dpdk.org
To: dev@dpdk.org
Subject: [Bug 959] tsc hz not matching kernel reported tcs frequency
Date: Wed, 16 Mar 2022 12:58:18 +0000
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X-Bugzilla-Component: core
X-Bugzilla-Version: 21.11
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https://bugs.dpdk.org/show_bug.cgi?id=3D959

            Bug ID: 959
           Summary: tsc hz not matching kernel reported tcs frequency
           Product: DPDK
           Version: 21.11
          Hardware: x86
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: core
          Assignee: dev@dpdk.org
          Reporter: maria.lingemark@ericsson.com
  Target Milestone: ---

On some machines the dpdk value of tsc hz does not match the kernel value.

The effect of this can be observed by writing a small test program that
measures elapsed time using two different sources.

The issue has been shown by taking clock_gettime() and rte_get_tsc_cycles(),
sleep, and then fetch the time stamps again with clock_gettime() and
rte_get_tsc_cycles().

When calculating the time from the two sources we notice a difference of ~2=
.3
ms per second.

Example from a test run with 1 second sleep:

rte_get_tsc_hz=3D2400000000
clock_gettime=3D1000056 us, tsc_time=3D997708 us, diff=3D2348 us

Info from dmesg:
tsc: Refined TSC clocksource calibration: 2394.365 MHz

We don't see the time difference on=20
Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz
Linux kernel 4.13.0-16-generic

but we do observe it on=20
Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz
Linux kernel 5.4.0-100-generic

--=20
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