linux-kernel - Re: [PATCH v2] perf, x86: Fix event scheduler for constraints with overlapping counters

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110901141219.GA13447@erda.amd.com>
Date:	Thu, 1 Sep 2011 16:12:19 +0200
From:	Robert Richter <robert.richter@....com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] perf, x86: Fix event scheduler for constraints with
 overlapping counters

On 01.09.11 08:56:46, Peter Zijlstra wrote:
> On Fri, 2011-05-20 at 05:18 +0200, Robert Richter wrote:
> > On 19.05.11 14:06:50, Ingo Molnar wrote:
> > > * Peter Zijlstra <peterz@...radead.org> wrote:
> > > 
> > > > On Wed, 2011-05-18 at 23:20 +0200, Ingo Molnar wrote:
> > > > > * Peter Zijlstra <peterz@...radead.org> wrote:
> > > > > 
> > > > > > >                         if (c->weight != w)
> > > > > > >                                 continue;
> > > > > > >  
> > > > > > > -                       for_each_set_bit(j, c->idxmsk, X86_PMC_IDX_MAX) {
> > > > > > > -                               if (!test_bit(j, used_mask))
> > > > > > > +                       /* for each bit in idxmsk starting from idx */
> > > > > > > +                       while (idx < X86_PMC_IDX_MAX) {
> > > > > > > +                               idx = find_next_bit(c->idxmsk, X86_PMC_IDX_MAX,
> > > > > > > +                                                   idx);
> > > > > > 
> > > > > > I'd be mighty tempted to ignore that 80 column rule here ;-)
> > > > > 
> > > > > Please put the body of the loop into a helper function, the function is large 
> > > > > and there are countless col80 uglinesses in it!
> > > > 
> > > > I just tried that, its real ugly due to the amount of state you need to
> > > > pass around.
> > > 
> > > Does it help if you put that state into a helper structure?
> > 
> > Yes, this is what I have in mind too. We could iterate on such a state
> > stucture instead of a couple of single variables. Storing and
> > restoring the state will then just copying the structure.
> 
> Any word on this work? I just noticed we actually need this for Intel
> too, the fixed purpose events have overlapping but non-identical
> constraint masks.
> 
> Now we could optimize the Intel case by always iterating from the top
> down, but it won't cure all cases. For example, suppose one counter
> (that could be on a FP reg) previously got scheduled on a GP register
> and we take the fast-path, in that case we would still end up
> under-utilized.

Yes, I had this patch in mind too. Will try to post an updated version
next week. Ok?

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/