From: Christoph Lameter <cl@linux.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>,
Pekka Enberg <penberg@cs.helsinki.fi>,
Minchan Kim <minchan.kim@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Greg KH <greg@kroah.com>,
Linux Driver Project <devel@driverdev.osuosl.org>,
linux-mm <linux-mm@kvack.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 03/10] Use percpu stats
Date: Tue, 31 Aug 2010 16:35:37 -0500 (CDT) [thread overview]
Message-ID: <alpine.DEB.2.00.1008311635100.867@router.home> (raw)
In-Reply-To: <1283290106.2198.26.camel@edumazet-laptop>
On Tue, 31 Aug 2010, Eric Dumazet wrote:
> > Yes, this_cpu_add() seems sufficient. I can't recall why I used u64_stats_*
> > but if it's not required for atomic access to 64-bit then why was it added to
> > the mainline in the first place?
>
> Because we wanted to have fast 64bit counters, even on 32bit arches, and
> this has litle to do with 'atomic' on one entity, but a group of
> counters. (check drivers/net/loopback.c, lines 91-94). No lock prefix
> used in fast path.
>
> We also wanted readers to read correct values, not a value being changed
> by a writer, with inconsistent 32bit halves. SNMP applications want
> monotonically increasing counters.
>
> this_cpu_add()/this_cpu_read() doesnt fit.
>
> Even for single counter, this_cpu_read(64bit) is not using an RMW
> (cmpxchg8) instruction, so you can get very strange results when low
> order 32bit wraps.
How about fixing it so that everyone benefits?
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2010-08-31 21:35 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-09 17:26 [PATCH 00/10] zram: various improvements and cleanups Nitin Gupta
2010-08-09 17:26 ` [PATCH 01/10] Replace ioctls with sysfs interface Nitin Gupta
2010-08-09 18:34 ` Pekka Enberg
2010-08-10 3:06 ` Nitin Gupta
2010-08-31 23:06 ` Dave Hansen
2010-08-09 17:26 ` [PATCH 02/10] Remove need for explicit device initialization Nitin Gupta
2010-08-09 18:36 ` Pekka Enberg
2010-08-10 3:38 ` Nitin Gupta
2010-08-09 17:26 ` [PATCH 03/10] Use percpu stats Nitin Gupta
2010-08-09 18:44 ` Pekka Enberg
2010-08-10 4:34 ` Andrew Morton
2010-08-11 16:39 ` Nitin Gupta
2010-08-11 17:18 ` Andrew Morton
2010-08-30 16:20 ` Christoph Lameter
2010-08-31 20:31 ` Nitin Gupta
2010-08-31 21:28 ` Eric Dumazet
2010-08-31 21:35 ` Christoph Lameter [this message]
2010-08-31 21:41 ` Eric Dumazet
2010-09-01 20:05 ` Christoph Lameter
2010-09-01 20:38 ` Eric Dumazet
2010-09-02 0:34 ` Christoph Lameter
2010-08-31 5:36 ` Anton Blanchard
2010-09-01 3:41 ` Anton Blanchard
2010-09-01 3:51 ` Anton Blanchard
2010-09-17 20:59 ` Andrew Morton
2010-08-09 17:26 ` [PATCH 04/10] Use percpu buffers Nitin Gupta
2010-08-09 18:57 ` Pekka Enberg
2010-08-10 4:47 ` Nitin Gupta
2010-08-10 5:05 ` Pekka Enberg
2010-08-10 5:32 ` Nitin Gupta
2010-08-10 7:36 ` Pekka Enberg
2010-08-09 17:26 ` [PATCH 05/10] Reduce per table entry overhead by 4 bytes Nitin Gupta
2010-08-09 18:59 ` Pekka Enberg
2010-08-10 4:55 ` Nitin Gupta
2010-08-09 17:26 ` [PATCH 06/10] Block discard support Nitin Gupta
2010-08-09 19:03 ` Pekka Enberg
2010-08-10 2:23 ` Jens Axboe
2010-08-10 4:54 ` Nitin Gupta
2010-08-10 15:54 ` Jens Axboe
2010-08-09 17:26 ` [PATCH 07/10] Increase compressed page size threshold Nitin Gupta
2010-08-09 18:32 ` Pekka Enberg
2010-08-09 17:26 ` [PATCH 08/10] Some cleanups Nitin Gupta
2010-08-09 19:02 ` Pekka Enberg
2010-08-09 17:26 ` [PATCH 09/10] Update zram documentation Nitin Gupta
2010-08-09 17:26 ` [PATCH 10/10] Document sysfs entries Nitin Gupta
2010-08-09 19:02 ` Pekka Enberg
2010-08-31 22:37 ` [PATCH 00/10] zram: various improvements and cleanups Greg KH
2010-09-01 3:32 ` Anton Blanchard
2010-09-09 17:24 ` OOM panics with zram Dave Hansen
2010-09-09 19:07 ` [patch -rc] oom: always return a badness score of non-zero for eligible tasks David Rientjes
2010-09-09 19:48 ` Dave Hansen
2010-09-09 21:00 ` David Rientjes
2010-09-09 21:10 ` Dave Hansen
2010-09-09 21:40 ` David Rientjes
2010-10-03 18:41 ` OOM panics with zram Nitin Gupta
2010-10-03 19:27 ` Dave Hansen
2010-10-03 19:40 ` Nitin Gupta
2010-10-04 11:08 ` Ed Tomlinson
2010-10-05 23:43 ` Greg KH
2010-10-06 2:29 ` Nitin Gupta
2010-10-06 2:36 ` Greg KH
2010-10-06 4:30 ` Nitin Gupta
2010-10-06 7:38 ` Pekka Enberg
2010-10-06 14:03 ` Greg KH
2010-10-06 14:16 ` Pekka Enberg
2010-10-06 14:53 ` Nitin Gupta
2010-10-06 14:02 ` Greg KH
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=alpine.DEB.2.00.1008311635100.867@router.home \
--to=cl@linux.com \
--cc=akpm@linux-foundation.org \
--cc=devel@driverdev.osuosl.org \
--cc=eric.dumazet@gmail.com \
--cc=greg@kroah.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=minchan.kim@gmail.com \
--cc=ngupta@vflare.org \
--cc=penberg@cs.helsinki.fi \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox