commit: 57779dc2b3b75bee05ef5d1ada47f615f7a13932 From: Alok Kataria <[email protected]> Date: Tue, 21 Feb 2012 18:19:55 -0800 Subject: x86, tsc: Skip refined tsc calibration on systems with reliable TSC
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 <[email protected]> Cc: John Stultz <[email protected]> Cc: Dirk Brandewie <[email protected]> Cc: Alan Cox <[email protected]> Cc: [email protected] [jstultz: Reworked to simply not schedule the refining work, rather then scheduling the work and bombing out later] Signed-off-by: John Stultz <[email protected]> --- arch/x86/kernel/tsc.c | 10 ++++++++++ 1 files changed, 10 insertions(+), 0 deletions(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index a62c201..6fcfcb3 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -932,6 +932,16 @@ 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; } -- 1.7.3.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
