linux-kernel - Re: [PATCH Resend] epoll: add EPOLLEXCLUSIVE support

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Message-ID: <20120329155323.GB2424@redhat.com>
Date:	Thu, 29 Mar 2012 11:53:24 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Hagen Paul Pfeifer <hagen@...u.net>
Cc:	richard -rw- weinberger <richard.weinberger@...il.com>,
	torvalds@...ux-foundation.org, LKML <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH Resend] epoll: add EPOLLEXCLUSIVE support

On Thu, Mar 29, 2012 at 05:05:41PM +0200, Hagen Paul Pfeifer wrote:
> * Jason Baron | 2012-03-29 10:16:53 [-0400]:
> 
> >Right, for level triggered events, they all wait up. However, if you use
> >edge triggered, ie add 'EPOLLET', then the event gets 'consumed' by the
> >first thread that wakes up, and the subseqent waiters wouldn't get woken
> >up. IE you'll get one wakeup.
> 
> I addressed level triggered, right - it match the model. But I don't wanted to
> wake up every every thread anyway. I don't want to abandon level triggered
> functioning.
> 
> Any objective against this flag?
> 

I was trying to better understand the use-case, since at least for the
test case you posted, 'EPOLLET', already does what you want.

Also, the 'EPOLLEXCLUSIVE' flag in your patch addresses multiple threads
blocking on *different* epoll fds. However, if multiple threads are
blocked on a single epoll fd, they will all be woken even if 'EPOLLEXCLUSIVE'
is set. Shouldn't 'EPOLLEXCLUSIVE' affect that case too?

Thanks,

-Jason
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