From: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <cl@linux.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
Andi Kleen <andi@firstfloor.org>, Ingo Molnar <mingo@elte.hu>,
Jens Axboe <axboe@kernel.dk>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Rik van Riel <riel@redhat.com>,
Linux Memory Management List <linux-mm@kvack.org>,
linux-fsdevel@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 6/9] readahead: add /debug/readahead/stats
Date: Fri, 27 Jan 2012 12:15:51 -0800 [thread overview]
Message-ID: <20120127121551.acd256aa.akpm@linux-foundation.org> (raw)
In-Reply-To: <alpine.DEB.2.00.1201271006480.16756@router.home>
On Fri, 27 Jan 2012 10:21:36 -0600 (CST)
Christoph Lameter <cl@linux.com> wrote:
> > +
> > +static void readahead_stats_reset(void)
> > +{
> > + int i, j;
> > +
> > + for (i = 0; i < RA_PATTERN_ALL; i++)
> > + for (j = 0; j < RA_ACCOUNT_MAX; j++)
> > + percpu_counter_set(&ra_stat[i][j], 0);
>
> for_each_online(cpu)
> memset(per_cpu_ptr(&ra_stat, cpu), 0, sizeof(ra_stat));
for_each_possible_cpu(). And that's one reason to not open-code the
operation. Another is so we don't have tiresome open-coded loops all
over the place.
But before doing either of those things we should choose boring old
atomic_inc(). Has it been shown that the cost of doing so is
unacceptable? Bearing this in mind:
> The accounting code will be compiled in by default
> (CONFIG_READAHEAD_STATS=y), and will remain inactive by default.
I agree with those choices. They effectively mean that the stats will
be a developer-only/debugger-only thing. So even if the atomic_inc()
costs are measurable during these develop/debug sessions, is anyone
likely to care?
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WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <cl@linux.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
Andi Kleen <andi@firstfloor.org>, Ingo Molnar <mingo@elte.hu>,
Jens Axboe <axboe@kernel.dk>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Rik van Riel <riel@redhat.com>,
Linux Memory Management List <linux-mm@kvack.org>,
linux-fsdevel@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 6/9] readahead: add /debug/readahead/stats
Date: Fri, 27 Jan 2012 12:15:51 -0800 [thread overview]
Message-ID: <20120127121551.acd256aa.akpm@linux-foundation.org> (raw)
In-Reply-To: <alpine.DEB.2.00.1201271006480.16756@router.home>
On Fri, 27 Jan 2012 10:21:36 -0600 (CST)
Christoph Lameter <cl@linux.com> wrote:
> > +
> > +static void readahead_stats_reset(void)
> > +{
> > + int i, j;
> > +
> > + for (i = 0; i < RA_PATTERN_ALL; i++)
> > + for (j = 0; j < RA_ACCOUNT_MAX; j++)
> > + percpu_counter_set(&ra_stat[i][j], 0);
>
> for_each_online(cpu)
> memset(per_cpu_ptr(&ra_stat, cpu), 0, sizeof(ra_stat));
for_each_possible_cpu(). And that's one reason to not open-code the
operation. Another is so we don't have tiresome open-coded loops all
over the place.
But before doing either of those things we should choose boring old
atomic_inc(). Has it been shown that the cost of doing so is
unacceptable? Bearing this in mind:
> The accounting code will be compiled in by default
> (CONFIG_READAHEAD_STATS=y), and will remain inactive by default.
I agree with those choices. They effectively mean that the stats will
be a developer-only/debugger-only thing. So even if the atomic_inc()
costs are measurable during these develop/debug sessions, is anyone
likely to care?
next prev parent reply other threads:[~2012-01-27 20:15 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-27 3:05 [PATCH 0/9] readahead stats/tracing, backwards prefetching and more (v4) Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` [PATCH 1/9] readahead: make context readahead more conservative Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` [PATCH 2/9] readahead: record readahead patterns Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` [PATCH 3/9] readahead: tag mmap page fault call sites Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` [PATCH 4/9] readahead: tag metadata " Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` [PATCH 5/9] readahead: add vfs/readahead tracing event Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` [PATCH 6/9] readahead: add /debug/readahead/stats Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 16:21 ` Christoph Lameter
2012-01-27 16:21 ` Christoph Lameter
2012-01-27 20:15 ` Andrew Morton [this message]
2012-01-27 20:15 ` Andrew Morton
2012-01-29 5:07 ` Wu Fengguang
2012-01-29 5:07 ` Wu Fengguang
2012-01-30 4:02 ` Dave Chinner
2012-01-30 4:02 ` Dave Chinner
2012-01-27 3:05 ` [PATCH 7/9] readahead: basic support for backwards prefetching Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` [PATCH 8/9] readahead: dont do start-of-file readahead after lseek() Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` [PATCH 9/9] readahead: snap readahead request to EOF Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-01-27 3:05 ` Wu Fengguang
2012-02-09 3:22 ` [PATCH 6/9 update changelog] readahead: add /debug/readahead/stats Wu Fengguang
2012-02-09 3:22 ` Wu Fengguang
-- strict thread matches above, loose matches on Subject: below --
2012-02-11 4:31 [PATCH 0/9] readahead stats/tracing, backwards prefetching and more (v5) Wu Fengguang
2012-02-11 4:31 ` [PATCH 6/9] readahead: add /debug/readahead/stats Wu Fengguang
2012-02-11 4:31 ` Wu Fengguang
2012-02-11 4:31 ` Wu Fengguang
2011-11-29 13:09 [PATCH 0/9] readahead stats/tracing, backwards prefetching and more (v2) Wu Fengguang
2011-11-29 13:09 ` [PATCH 6/9] readahead: add /debug/readahead/stats Wu Fengguang
2011-11-29 13:09 ` Wu Fengguang
2011-11-29 13:09 ` Wu Fengguang
2011-11-29 15:21 ` Jan Kara
2011-11-29 15:21 ` Jan Kara
2011-11-30 0:44 ` Wu Fengguang
2011-11-30 0:44 ` Wu Fengguang
2011-12-14 6:36 ` Wu Fengguang
2011-12-14 6:36 ` Wu Fengguang
2011-12-19 16:32 ` Jan Kara
2011-12-19 16:32 ` Jan Kara
2011-12-21 1:29 ` Wu Fengguang
2011-12-21 1:29 ` Wu Fengguang
2011-12-21 4:06 ` Dave Chinner
2011-12-21 4:06 ` Dave Chinner
2011-12-23 3:33 ` Wu Fengguang
2011-12-23 3:33 ` Wu Fengguang
2011-12-23 11:16 ` Jan Kara
2011-12-23 11:16 ` Jan Kara
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