From: patrickg <patrickg@supermicro.com>
To: "Brown, Len" <len.brown@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: "mingo@kernel.org" <mingo@kernel.org>,
"Du, Alek" <alek.du@intel.com>,
"arjan@linux.intel.com" <arjan@linux.intel.com>,
"Tang, Feng" <feng.tang@intel.com>
Subject: Re: [RFC] x86, tsc: Add kcmdline args for skipping tsc calibration sequences
Date: Tue, 24 Jul 2018 12:45:22 -0700 [thread overview]
Message-ID: <cb798dcd-8cd6-8a92-9f6c-50bec0afe204@supermicro.com> (raw)
In-Reply-To: <c7582a8c-8cc1-eff3-2452-a8d42d23fea1@supermicro.com>
K, did significant poking.
native_calibrate_cpu is getting precidence no matter what because on SKL server, native_calibrate_tsc is always returning zero (Note that there is a caveat 2 lines down).
In native_calibrate_tsc, I'm seeing it always return zero after the `switch (boot_cpu_data.x86_model)`. crystal_khz is zero so it rolls through that, never assigns it.
Now I'm apparently not testing on production CPU's. I've requested that they drop em' in so I can ensure `CPUID 15H TSC/Crystal ratio` doesn't differ between the ES and Prod silicon, since that will effect the math
Anyways, Then after calibrate is found to be zero, it's utilizing the CPUID calculation from native_calibrate_cpu for tsc_khz since that's returning a 'proper' value when it does the reassignment:
---
if (tsc_khz == 0) /* Hits here and reassigns tsc_khz to the cpuid calculation. */
tsc_khz = cpu_khz;
else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz)
cpu_khz = tsc_khz;
---
I'll post another update when I've checked with Prod CPU's, /probably/ tomorrow.
next prev parent reply other threads:[~2018-07-24 19:45 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-13 19:19 patrickg
2018-07-13 19:40 ` Arjan van de Ven
2018-07-13 19:54 ` patrickg
2018-07-13 19:54 ` patrickg
2018-07-14 2:40 ` Brown, Len
2018-07-20 22:27 ` patrickg
2018-07-24 19:45 ` patrickg [this message]
2018-07-26 19:21 ` patrickg
2018-08-16 17:28 ` patrickg
2018-10-25 17:12 ` patrickg
2018-10-25 18:01 ` Prarit Bhargava
2018-10-25 19:13 ` patrickg
2018-12-03 19:37 ` Patrick Geary
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