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Subject: Re: [PATCH] af_unix: unix_write_space() use keyed wakeups
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Alban Crequy <alban.crequy@collabora.co.uk>
Cc: Pauli Nieminen <pauli.nieminen@collabora.co.uk>,
        Davide Libenzi <davidel@xmailserver.org>,
        "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@vger.kernel.org, Rainer Weikusat <rweikusat@mssgmbh.com>
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Date: Wed, 24 Nov 2010 01:28:11 +0100
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Le mercredi 24 novembre 2010 à 00:20 +0000, Alban Crequy a écrit :
> Le Wed, 24 Nov 2010 01:27:56 +0200,
> Pauli Nieminen <pauli.nieminen@collabora.co.uk> a écrit :
> 
> > ----- Original message -----
> > > Le Sat, 30 Oct 2010 08:44:44 +0200,
> > > Eric Dumazet <eric.dumazet@gmail.com> a écrit :
> > > 
> > > > We still loop on 800 items, on each
> > > > wake_up_interruptible_sync_poll() call, so maybe we want to
> > > > optimize this later, adding a global key, ORing all items keys. I
> > > > dont think its worth the added complexity, given the biased usage
> > > > of your program (800 'listeners' to one event). Is it a real life
> > > > scenario ?
> > > 
> > > Pauli Nieminen told me about his performance problem in select() so
> > > I wrote the test program but I don't know what exactly is the real
> > > life scenario.
> > > 
> > 
> > Real world scenario is xsever that has tens client connections to
> > manage. When xserver is happily sleeping at seclect call some client
> > reading events/replies from server triggers in kernel looping over
> > all xserver fds. xserver isn't waiting for socket to became writeable
> > in ussual cases so kernel schedules back to client.
> 
> But are they SOCK_STREAM or SOCK_DGRAM sockets? The patches fix
> performances with SOCK_DGRAM. If the xserver scenario is with
> SOCK_STREAM sockets, your problem is probably still unfixed.
> 


It should not matter ?

commit 67426b756c4d52c51 (af_unix: use keyed wakeups ) makes
unix_write_space() call wake_up_interruptible_sync_poll() instead of
wake_up_interruptible_sync().

So it should be fixed for both STREAM/DGRAM sockets ?