Messages in this thread | | | Date | Mon, 24 Aug 2009 10:30:53 +0800 | Subject | Re: [RFC patch] need check TSC wrap unconditionally | From | Luming Yu <> |
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On Sat, Aug 22, 2009 at 12:37 AM, Peter Zijlstra<peterz@infradead.org> wrote: > On Fri, 2009-08-14 at 12:15 +0800, Luming Yu wrote: >> Hi there, > > Hi, thanks for CC'ing the right folks. > >> we disabled tsc wrap check on any platform that has NOSTOP_TSC cpu. But this >> will cause some real problem.For example, 1.CPU does has constant and >> non_stop tsc, which means different CPU ticks at same rate in same domain,but >> have been given different initial TSC value.Then at any given time, >> CPUsare unsynchronized. >> 2. if those CPUs are sit in different domain..(multi-chassis cluster system?) >> >> Please review. If make sense, please apply. > > Right, so because your machine is funny, everybody with a good machine > should suffer?
How comes? Good machine will pass the check without any problem.
> > If the TSCs run at identical frequency (one time domain) but at > different offsets, you can fix that by using cyc2ns_offset.
iirc, in old kernel, there was a function trying to re-sync TSC. But it has been removed.. Should I re-introduce something that has been deleted. It is odd to do such kind of thing to me if I don't know why it was deleted.
> > When the machine has unsynchonized frequencies (multiple time domains), > detect that during cpu enumeration and use that to disable the > optimization.
yes.
> >> Signed-off-by: Yu Luming <luming.yu@intel.com> > >> arch/x86/kernel/tsc_sync.c | 7 +------ >> 1 file changed, 1 insertion(+), 6 deletions(-) >> >> diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c >> index 027b5b4..312ba84 100644 >> --- a/arch/x86/kernel/tsc_sync.c >> +++ b/arch/x86/kernel/tsc_sync.c >> @@ -113,11 +113,6 @@ void __cpuinit check_tsc_sync_source(int cpu) >> if (unsynchronized_tsc()) >> return; >> >> - if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) { >> - pr_info("Skipping synchronization checks as TSC is >> reliable.\n"); >> - return; >> - } >> - >> pr_info("checking TSC synchronization [CPU#%d -> CPU#%d]:", >> smp_processor_id(), cpu); >> >> @@ -171,7 +166,7 @@ void __cpuinit check_tsc_sync_target(void) >> { >> int cpus = 2; >> >> - if (unsynchronized_tsc() || boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) >> + if (unsynchronized_tsc()) >> return; >> >> /* > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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