This is a note to let you know that I've just added the patch titled
x86/tsc: Fix erroneous TSC rate on Skylake Xeon
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: x86-tsc-fix-erroneous-tsc-rate-on-skylake-xeon.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From b511203093489eb1829cb4de86e8214752205ac6 Mon Sep 17 00:00:00 2001
From: Len Brown len.brown@intel.com Date: Fri, 22 Dec 2017 00:27:55 -0500 Subject: x86/tsc: Fix erroneous TSC rate on Skylake Xeon
From: Len Brown len.brown@intel.com
commit b511203093489eb1829cb4de86e8214752205ac6 upstream.
The INTEL_FAM6_SKYLAKE_X hardcoded crystal_khz value of 25MHZ is problematic:
- SKX workstations (with same model # as server variants) use a 24 MHz crystal. This results in a -4.0% time drift rate on SKX workstations.
- SKX servers subject the crystal to an EMI reduction circuit that reduces its actual frequency by (approximately) -0.25%. This results in -1 second per 10 minute time drift as compared to network time.
This issue can also trigger a timer and power problem, on configurations that use the LAPIC timer (versus the TSC deadline timer). Clock ticks scheduled with the LAPIC timer arrive a few usec before the time they are expected (according to the slow TSC). This causes Linux to poll-idle, when it should be in an idle power saving state. The idle and clock code do not graciously recover from this error, sometimes resulting in significant polling and measurable power impact.
Stop using native_calibrate_tsc() for INTEL_FAM6_SKYLAKE_X. native_calibrate_tsc() will return 0, boot will run with tsc_khz = cpu_khz, and the TSC refined calibration will update tsc_khz to correct for the difference.
[ tglx: Sanitized change log ]
Fixes: 6baf3d61821f ("x86/tsc: Add additional Intel CPU models to the crystal quirk list") Signed-off-by: Len Brown len.brown@intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: peterz@infradead.org Cc: Prarit Bhargava prarit@redhat.com Link: https://lkml.kernel.org/r/ff6dcea166e8ff8f2f6a03c17beab2cb436aa779.151392041... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/tsc.c | 1 - 1 file changed, 1 deletion(-)
--- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -693,7 +693,6 @@ unsigned long native_calibrate_tsc(void) case INTEL_FAM6_KABYLAKE_DESKTOP: crystal_khz = 24000; /* 24.0 MHz */ break; - case INTEL_FAM6_SKYLAKE_X: case INTEL_FAM6_ATOM_DENVERTON: crystal_khz = 25000; /* 25.0 MHz */ break;
Patches currently in stable-queue which might be from len.brown@intel.com are
queue-4.9/x86-tsc-fix-erroneous-tsc-rate-on-skylake-xeon.patch