linux-kernel - Re: The thundering herd like problem when multi epolls on one fd

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Date:	Sat, 14 Jan 2012 16:57:13 +0100
From:	Hagen Paul Pfeifer <hagen@...u.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Li Yu <raise.sail@...il.com>, linux-kernel@...r.kernel.org,
	davidel@...ilserver.org
Subject: Re: The thundering herd like problem when multi epolls on one fd

* Eric Dumazet | 2012-01-14 14:20:47 [+0100]:

>What happens if the awaken thread does not consume the event, and prefer
>to exit ?
>
>If several threads are doing select()/poll()/epoll() on a shared fd,
>they _all_ must be notified the fd is ready, as manpages claim.
>

And if it is intended? Signaled via a new epoll_ctl() epoll_event flag? E.g.
EPOLLEXCLUSIVE

>Doing otherwise would require the prior consent of the user, using a
>special flag for example, and documentation.

Oops, yes. A fanout like mechanism _may be_ superior, but I think tests will
show some improvements anyway.

Hagen
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