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

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Message-ID: <CABPqkBQMi5NoL1EFB8ajopF8QbF3kiFgk6NkSkaqzruVaEQJOQ@mail.gmail.com>
Date:	Thu, 5 Jun 2014 14:55:05 +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 2:50 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?
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