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Date: Wed, 22 Oct 2014 16:58:04 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: Stephane Eranian <eranian@google.com>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@elte.hu,
        ak@linux.intel.com, kan.liang@intel.com, bp@alien8.de,
        maria.n.dimakopoulou@gmail.com
Subject: Re: [PATCH v2 11/12] perf/x86: make HT bug workaround conditioned on
 HT enabled
Message-ID: <20141022145804.GC15126@krava.brq.redhat.com>
References: <1412872486-2930-1-git-send-email-eranian@google.com>
 <1412872486-2930-12-git-send-email-eranian@google.com>
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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