linux-kernel - Re: [PATCH 9/9] perf/x86: add syfs entry to disable HT bug workaround

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Date:	Thu, 5 Jun 2014 15:16:47 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Matt Fleming <matt@...sole-pimps.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Jiri Olsa <jolsa@...hat.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>,
	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
Subject: Re: [PATCH 9/9] perf/x86: add syfs entry to disable HT bug workaround

On Thu, Jun 5, 2014 at 2:59 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Jun 05, 2014 at 02:55:05PM +0200, Stephane Eranian wrote:
>> On Thu, Jun 5, 2014 at 2:50 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>> > On Thu, Jun 05, 2014 at 12:16:01PM +0100, Matt Fleming wrote:
>> >> On 5 June 2014 11:19, Stephane Eranian <eranian@...gle.com> wrote:
>> >> > How would you know that you have a uniform workload from inside
>> >> > the kernel?
>> >>
>> >> That's what I'm asking you ;-)
>> >>
>> >> >> Does cpu_sibling_map not give you some indication of whether HT is
>> >> >> enabled? I think the topology_thread_cpumask() is the topology API for
>> >> >> that. But I could most definitely be wrong. Hopefully someone on the
>> >> >> Cc list will know.
>> >> >>
>> >> > Remember trying some of that, but when perf_event is initialized, those
>> >> > masks are not yet setup properly.
>> >>
>> >> Oh, bummer.
>> >
>> > So we init perf very early to get nmi-watchdog up and running, but
>> > there's no reason you cannot register a second initcall later and flip
>> > the switch from it there.
>>
>> and what initcall would that be?
>
> Pretty much anything !early_initcall() is ran after SMP bringup iirc.

Ok, we can try this. Need to check the impact on NMI watchdog if
already active.
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