linux-kernel - Re: [PATCH] rfc: threaded epoll

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Date:	Sat, 05 May 2007 06:15:02 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Davi Arnaut <davi@...ent.com.br>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rfc: threaded epoll_wait thundering herd

Davi Arnaut a écrit :
> 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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