LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Eric Dumazet <dada1@cosmosbay.com>
To: Andrea Arcangeli <andrea@suse.de>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>,
	Anton Blanchard <anton@samba.org>, Rik van Riel <riel@redhat.com>,
	Lorenzo Allegrucci <l_allegrucci@yahoo.it>,
	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
	Suparna Bhattacharya <suparna@in.ibm.com>,
	Jens Axboe <jens.axboe@oracle.com>
Subject: Re: SMP performance degradation with sysbench
Date: Tue, 13 Mar 2007 13:02:44 +0100	[thread overview]
Message-ID: <200703131302.45216.dada1@cosmosbay.com> (raw)
In-Reply-To: <20070313114215.GI8992@v2.random>

On Tuesday 13 March 2007 12:42, Andrea Arcangeli wrote:

> My wild guess is that they're allocating memory after taking
> futexes. If they do, something like this will happen:
>
>      taskA		taskB		taskC
>      user lock
> 			mmap_sem lock
>      mmap sem -> schedule
> 					user lock -> schedule
>
> If taskB wouldn't be there triggering more random trashing over the
> mmap_sem, the lock holder wouldn't wait and task C wouldn't wait too.
>
> I suspect the real fix is not to allocate memory or to run other
> expensive syscalls that can block inside the futex critical sections...

glibc malloc uses arenas, and trylock() only. It should not block because if 
an arena is already locked, thread automatically chose another arena, and 
might create a new one if necessary.

But yes, mmap_sem contention is a big problem, because it's also taken by 
futex code (unfortunately)


  reply	other threads:[~2007-03-13 12:02 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-25 17:44 Lorenzo Allegrucci
2007-02-25 23:46 ` Rik van Riel
2007-02-26 13:36   ` Nick Piggin
2007-02-26 13:41     ` Nick Piggin
2007-02-26 22:04     ` Pete Harlan
2007-02-26 22:36       ` Dave Jones
2007-02-27  0:32         ` Hiro Yoshioka
2007-02-27  0:43           ` Rik van Riel
2007-02-27  4:03             ` Hiro Yoshioka
2007-02-27  4:31               ` Rik van Riel
2007-02-27  8:14                 ` J.A. Magallón
2007-02-27 14:02                   ` Rik van Riel
2007-02-27 14:56                     ` Paulo Marques
2007-02-27 20:40                       ` Nish Aravamudan
2007-02-28  2:21                       ` Bill Davidsen
2007-02-28  2:52                         ` Nish Aravamudan
2007-03-01  0:20                           ` Nish Aravamudan
2007-02-27 19:05                     ` Lorenzo Allegrucci
2007-03-01 16:57                       ` Lorenzo Allegrucci
2007-02-28  1:27     ` Nish Aravamudan
2007-02-28  2:22       ` Nick Piggin
2007-02-28  2:51         ` Nish Aravamudan
2007-03-12 22:00     ` Anton Blanchard
2007-03-13  5:11       ` Nick Piggin
2007-03-13  9:45         ` Andrea Arcangeli
2007-03-13 10:06           ` Nick Piggin
2007-03-13 10:31             ` Andrea Arcangeli
2007-03-13 10:37               ` Nick Piggin
2007-03-13 10:57                 ` Andrea Arcangeli
2007-03-13 11:12                   ` Nick Piggin
2007-03-13 11:40                     ` Eric Dumazet
2007-03-13 11:56                       ` Nick Piggin
2007-03-13 11:42                     ` Andrea Arcangeli
2007-03-13 12:02                       ` Eric Dumazet [this message]
2007-03-13 12:27                         ` Jakub Jelinek
2007-03-13 12:08                       ` Nick Piggin
2007-03-14 23:33                         ` Siddha, Suresh B
2007-03-20  2:29                           ` Zhang, Yanmin
2007-04-02  2:59                             ` Zhang, Yanmin
2007-03-13  6:00       ` Eric Dumazet
2007-03-14  0:36       ` Nish Aravamudan
2007-03-14  1:00         ` Eric Dumazet
2007-03-14  1:09           ` Nish Aravamudan
     [not found] <fa.V3M3ZgXL+lFlIyhx43YxCU/JFUk@ifi.uio.no>
     [not found] ` <fa.ciL5lzdfskdJHJPgn+UVCHt/9EM@ifi.uio.no>
     [not found]   ` <fa.2ABbHhyCbp3Fx7hSE/Gr0SuzFvw@ifi.uio.no>
     [not found]     ` <fa.oaZk6Aiqd8gyZNsj7+m+w9MibhU@ifi.uio.no>
     [not found]       ` <fa.RjX9Y4ckjRCle5L+uWNdd0snOio@ifi.uio.no>
     [not found]         ` <fa.XocsudxlGplKh0kloTtA0juPwtA@ifi.uio.no>
2007-02-28  0:20           ` Robert Hancock
2007-02-28  1:32             ` Hiro Yoshioka

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=200703131302.45216.dada1@cosmosbay.com \
    --to=dada1@cosmosbay.com \
    --cc=andrea@suse.de \
    --cc=anton@samba.org \
    --cc=jens.axboe@oracle.com \
    --cc=l_allegrucci@yahoo.it \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@elte.hu \
    --cc=nickpiggin@yahoo.com.au \
    --cc=riel@redhat.com \
    --cc=suparna@in.ibm.com \
    --subject='Re: SMP performance degradation with sysbench' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).