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authorAlok Kataria <akataria@vmware.com>2012-02-21 18:19:55 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-04-02 09:53:09 -0700
commit94e75cfe69ac1d91bae5998ac0f21e355ce93a8b (patch)
parenteaadbfbf85875c76259c93e7ba51aebe2cad2138 (diff)
x86, tsc: Skip refined tsc calibration on systems with reliable TSC
commit 57779dc2b3b75bee05ef5d1ada47f615f7a13932 upstream. While running the latest Linux as guest under VMware in highly over-committed situations, we have seen cases when the refined TSC algorithm fails to get a valid tsc_start value in tsc_refine_calibration_work from multiple attempts. As a result the kernel keeps on scheduling the tsc_irqwork task for later. Subsequently after several attempts when it gets a valid start value it goes through the refined calibration and either bails out or uses the new results. Given that the kernel originally read the TSC frequency from the platform, which is the best it can get, I don't think there is much value in refining it. So for systems which get the TSC frequency from the platform we should skip the refined tsc algorithm. We can use the TSC_RELIABLE cpu cap flag to detect this, right now it is set only on VMware and for Moorestown Penwell both of which have there own TSC calibration methods. Signed-off-by: Alok N Kataria <akataria@vmware.com> Cc: John Stultz <johnstul@us.ibm.com> Cc: Dirk Brandewie <dirk.brandewie@gmail.com> Cc: Alan Cox <alan@linux.intel.com> [jstultz: Reworked to simply not schedule the refining work, rather then scheduling the work and bombing out later] Signed-off-by: John Stultz <john.stultz@linaro.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 10 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index db483369f10b..3fe298abc7cf 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -934,6 +934,16 @@ static int __init init_tsc_clocksource(void)
clocksource_tsc.rating = 0;
clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
+ /*
+ * Trust the results of the earlier calibration on systems
+ * exporting a reliable TSC.
+ */
+ if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {
+ clocksource_register_khz(&clocksource_tsc, tsc_khz);
+ return 0;
+ }
schedule_delayed_work(&tsc_irqwork, 0);
return 0;