leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

x86/tsc: Let high latency PIT fail fast in quick_pit_calibrate()

Browse Source 
If it takes longer than 12us to read the PIT counter lsb/msb,
then the error margin will never fall below 500ppm within 50ms,
and Fast TSC calibration will always fail.

This patch detects when that will happen and fails fast. Note
the failure message is not printed in that case because:
1. it will always happen on that class of hardware
2. the absence of the message is more informative than its
presence

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/556EB717.9070607@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Adrian Hunter 2015-06-03 10:39:46 +03:00 committed by Thomas Gleixner
parent d770e558e2
commit 5aac644a99
1 changed files with 10 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
arch/x86/kernel/tsc.c
View File

@ -598,10 +598,19 @@ static unsigned long quick_pit_calibrate(void)
if (!pit_expect_msb(0xff-i, &delta, &d2))
break;
delta -= tsc;
/*
* Extrapolate the error and fail fast if the error will
* never be below 500 ppm.
*/
if (i == 1 &&
d1 + d2 >= (delta * MAX_QUICK_PIT_ITERATIONS) >> 11)
return 0;
/*
* Iterate until the error is less than 500 ppm
*/
delta -= tsc;
if (d1+d2 >= delta >> 11)
continue;