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    SubjectRe: [PATCH v2 11/12] perf/x86: make HT bug workaround conditioned on HT enabled
    On Thu, Oct 09, 2014 at 06:34:45PM +0200, Stephane Eranian wrote:

    SNIP

    > --- a/arch/x86/kernel/cpu/perf_event_intel.c
    > +++ b/arch/x86/kernel/cpu/perf_event_intel.c
    > @@ -12,6 +12,7 @@
    > #include <linux/init.h>
    > #include <linux/slab.h>
    > #include <linux/export.h>
    > +#include <linux/watchdog.h>
    >
    > #include <asm/cpufeature.h>
    > #include <asm/hardirq.h>
    > @@ -1811,7 +1812,7 @@ intel_start_scheduling(struct cpu_hw_events *cpuc)
    > /*
    > * nothing needed if in group validation mode
    > */
    > - if (cpuc->is_fake)
    > + if (cpuc->is_fake || !is_ht_workaround_enabled())
    > return;
    > /*
    > * no exclusion needed
    > @@ -1849,8 +1850,9 @@ intel_stop_scheduling(struct cpu_hw_events *cpuc)
    > /*
    > * nothing needed if in group validation mode
    > */
    > - if (cpuc->is_fake)
    > + if (cpuc->is_fake || !is_ht_workaround_enabled())
    > return;


    Is it possible to change is_ht_workaround_enabled() result within
    intel_start_scheduling and intel_stop_scheduling time frame? like
    following would happen:


    is_ht_workaround_enabled == 1

    intel_start_scheduling -> spin_lock(&excl_cntrs->lock);

    # echo 0 > /sys/devices/cpu/ht_bug_workaround

    is_ht_workaround_enabled == 0

    intel_stop_scheduling -> wont call spin_unlock(&excl_cntrs->lock)


    for some reason I can't get HT enabled on my HSW server, so I cannot try ;-)

    jirka


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