linux-kernel - Re: [PATCH v2 0/12] perf/x86: implement HT leak workaround for SNB/IVB/HSW

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Message-ID: <20141022091239.GG12706@worktop.programming.kicks-ass.net>
Date:	Wed, 22 Oct 2014 11:12:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	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>,
	"Liang, Kan" <kan.liang@...el.com>, Borislav Petkov <bp@...en8.de>,
	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
Subject: Re: [PATCH v2 0/12] perf/x86: implement HT leak workaround for
 SNB/IVB/HSW

On Tue, Oct 21, 2014 at 03:08:32PM +0200, Stephane Eranian wrote:
> On Tue, Oct 21, 2014 at 3:03 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Tue, Oct 21, 2014 at 02:28:06PM +0200, Stephane Eranian wrote:
> >> Peter,
> >>
> >> On Tue, Oct 21, 2014 at 1:25 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> >> >
> >> >
> >> > lkml.kernel.org/r/CABPqkBRbst4sgpgE5O_VXt-CSC0VD=aP2KWA0e3Uy64tw7df3A@...l.gmail.com
> >> >
> >> > I missed that 3 lines if they were in here.
> >> >
> >> I did not put them in there because there is another problem.
> >> If you partition the generic counters 2 and 2, then some CPUs will not
> >> be able to measure some events.
> >> Unfortunately, there is no way to partition the 4 counters such that
> >> all the events can be measured by
> >> each CPU. Some events or precise sampling requires counter 2 for
> >> instance (like prec_dist).
> >> That's why I did not put this fix in.
> >
> > Ah, I wasn't thinking about a hard partition, just a limit on the number
> > of exclusive counters any one CPU can claim such as to not starve. Or is
> > that what you were talking about? I feel not being able to starve
> > another CPU is more important than a better utilization bound for
> > counter scheduling.
> 
> So you're saying, just limit number of used counters to 2 regardless
> of which one they are. 

used as in marked exclusive and forced empty on the other side.

> So sometimes, this will avoid the problem aforementioned and sometimes
> not. We can try that.

How will this sometimes not avoid the starvation issue?
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