From: Davide Libenzi <davidel@xmailserver.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Alban Crequy <alban.crequy@collabora.co.uk>,
"David S. Miller" <davem@davemloft.net>,
Stephen Hemminger <shemminger@vyatta.com>,
Cyrill Gorcunov <gorcunov@openvz.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
netdev@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Pauli Nieminen <pauli.nieminen@collabora.co.uk>,
Rainer Weikusat <rweikusat@mssgmbh.com>
Subject: Re: [PATCH 0/1] RFC: poll/select performance on datagram sockets
Date: Fri, 29 Oct 2010 14:57:28 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.00.1010291451330.8517@davide-lnx1> (raw)
In-Reply-To: <1288386348.2680.25.camel@edumazet-laptop>
On Fri, 29 Oct 2010, Eric Dumazet wrote:
> Following patch solves the problem for me, and its only a start, I am
> pretty sure we can optimize more than that.
>
> What I did is to move "struct poll_wqueues table;" out of do_select()
> in its caller. This structure is highly modified by an other cpu in
> Alban workload, and this slow down do_select() because many accesses to
> some of its local variables (normally, private ones !) hit a false
> sharing.
>
> Before :
>
> # time /root/uclient connected
> The performance problem will be triggered
> select: begin
> select: end: 3 seconds
>
> real 0m3.101s
> user 0m0.000s
> sys 0m6.104s
>
> After :
>
> # time /root/uclient connected
> The performance problem will be triggered
> select: begin
> select: end: 1 seconds
>
> real 0m1.041s
> user 0m0.004s
> sys 0m2.040s
>
>
> Impressive no ?
It is, though I am not sure that shuffling code around to chase false
sharing on very specific cases, is an approach worth following.
The new position of the table on the stack might share with another hot
line, under a different load.
- Davide
next prev parent reply other threads:[~2010-10-29 21:59 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-29 18:18 [PATCH 0/1] RFC: poll/select performance on datagram sockets Alban Crequy
2010-10-29 18:18 ` Alban Crequy
2010-10-29 18:21 ` [PATCH] " Alban Crequy
2010-10-29 19:27 ` [PATCH 0/1] RFC: " Eric Dumazet
2010-10-29 20:08 ` Davide Libenzi
2010-10-29 20:20 ` Eric Dumazet
2010-10-29 20:46 ` Davide Libenzi
2010-10-29 21:05 ` Eric Dumazet
2010-10-29 21:57 ` Davide Libenzi [this message]
2010-10-29 22:08 ` Eric Dumazet
2010-10-30 9:53 ` [PATCH] af_unix: optimize unix_dgram_poll() Eric Dumazet
2010-10-30 17:45 ` Davide Libenzi
2010-10-29 20:20 ` [PATCH 0/1] RFC: poll/select performance on datagram sockets Jesper Juhl
2010-10-29 20:40 ` David Miller
2010-10-29 20:45 ` Eric Dumazet
2010-10-30 6:44 ` [PATCH] af_unix: unix_write_space() use keyed wakeups Eric Dumazet
2010-10-30 15:03 ` Davide Libenzi
2010-11-08 21:44 ` David Miller
2010-10-30 21:36 ` Alban Crequy
[not found] ` <1290554876.2158.5.camel@Nokia-N900-51-1>
2010-11-24 0:20 ` Alban Crequy
2010-11-24 0:28 ` Eric Dumazet
2010-10-30 11:34 ` [PATCH 0/1] RFC: poll/select performance on datagram sockets Alban Crequy
2010-10-30 12:53 ` Eric Dumazet
2010-10-30 13:17 ` Eric Dumazet
[not found] ` <20101030224703.065e70f6@chocolatine.cbg.collabora.co.uk>
2010-10-31 15:36 ` [PATCH 1/2] af_unix: fix unix_dgram_poll() behavior for EPOLLOUT event Eric Dumazet
2010-10-31 19:07 ` Davide Libenzi
2010-11-08 21:44 ` David Miller
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