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    SubjectRe: [RFC patch] need check TSC wrap unconditionally
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    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?

    If the TSCs run at identical frequency (one time domain) but at
    different offsets, you can fix that by using cyc2ns_offset.

    When the machine has unsynchonized frequencies (multiple time domains),
    detect that during cpu enumeration and use that to disable the
    optimization.

    > 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;
    >
    > /*


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