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Message-Id: <1243584644.23657.164.camel@twins>
Date: Fri, 29 May 2009 10:10:44 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Paul Mackerras <paulus@...ba.org>
Cc: Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] perf_counter: Don't swap contexts containing
locked mutex
On Fri, 2009-05-29 at 10:06 +0200, Peter Zijlstra wrote:
> > @@ -919,7 +919,8 @@ static int context_equiv(struct perf_counter_context *ctx1,
> > struct perf_counter_context *ctx2)
> > {
> > return ctx1->parent_ctx && ctx1->parent_ctx == ctx2->parent_ctx
> > - && ctx1->parent_gen == ctx2->parent_gen;
> > + && ctx1->parent_gen == ctx2->parent_gen
> > + && ctx1->parent_gen != ~0ull;
> > }
>
> There's a nasty surprise for people a few generations down the line. All
> of a sudden performance drops for a while for some unknown reason, and
> then its good again,.. how odd ;-)
OK, so I was joking, but my brain just came up with:
static void inc_generation(struct perf_counter_ctx *ctx)
{
ctx->generation = ++ctx->generation & 0x7FFFFFFFFFFFFFFF;
}
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