Message-ID: <463C04C6.7000205@cosmosbay.com>
Date: Sat, 05 May 2007 06:15:02 +0200
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Davi Arnaut <davi@haxent.com.br>
CC: Andrew Morton <akpm@linux-foundation.org>,
       Davide Libenzi <davidel@xmailserver.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] rfc: threaded epoll_wait thundering herd
References: <20070504225730.490334000@haxent.com.br> <463BC3CA.6050109@haxent.com.br>
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Davi Arnaut a ?crit :
> Hi,
> 
> If multiple threads are parked on epoll_wait (on a single epoll fd) and
> events become available, epoll performs a wake up of all threads of the
> poll wait list, causing a thundering herd of processes trying to grab
> the eventpoll lock.
> 
> This patch addresses this by using exclusive waiters (wake one). Once
> the exclusive thread finishes transferring it's events, a new thread
> is woken if there are more events available.
> 
> Makes sense?
> 

Yes it makes sense.

But... what happens if the thread that was chosen exits from the loop in 
ep_poll() with res = -EINTR (because of signal_pending(current))


Me thinks in this case some ready events can wait forever (up to next 
ep_poll_callback() or another thread enters ep_poll())


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