Messages in this thread |  | | | Date | Mon, 6 Feb 2012 16:34:08 +0100 | | From | Borislav Petkov <> | | Subject | Re: [BUG] perf: perf sched warning possibly due to clock granularity on AMD |
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+ Andreas.
On Mon, Feb 06, 2012 at 03:26:43PM +0100, Peter Zijlstra wrote: > On Mon, 2012-02-06 at 14:25 +0100, Stephane Eranian wrote: > > In summary, two issues: > > - Why is sched_clock_stable not set or even tested on recent AMD systems?
AFAICT, sched_clock_stable is set on Intel under the following conditions:
/* * c->x86_power is 8000_0007 edx. Bit 8 is TSC runs at constant rate * with P/T states and does not stop in deep C-states. * * It is also reliable across cores and sockets. (but not across * cabinets - we turn it off in that case explicitly.) */ if (c->x86_power & (1 << 8)) { set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC); if (!check_tsc_unstable()) sched_clock_stable = 1; } and yes, we can do CONSTANT_TSC and NONSTOP_TSC on the now older F10h already, so Bulldozer can do that too, implicitly.
I don't see why sched_clock_stable shouldn't be moved to generic x86 code and set based on the two CPUID cap flags above.
HTH.
-- Regards/Gruss, Boris.
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