linux-kernel - Re: [PATCH 1/1] eventfd: implementation of EFD

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Date:	Fri, 8 Feb 2013 22:21:07 +0000
From:	Eric Wong <normalperson@...t.net>
To:	Martin Sustrik <sustrik@...bpm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Sha Zhengju <handai.szj@...bao.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] eventfd: implementation of EFD_MASK flag

Martin Sustrik <sustrik@...bpm.com> wrote:
> On 07/02/13 23:44, Andrew Morton wrote:
> >That's a nice changelog but it omitted a critical thing: why do you
> >think the kernel needs this feature?  What's the value and use case for
> >being able to poll these descriptors?
> 
> To address the question, I've written down detailed description of
> the challenges of the network protocol development in user space and
> how the proposed feature addresses the problems.
> 
> It's too long to fit into ChangeLog, but it may be worth reading
> when trying to judge the merit of the patch.
> 
> It can be found here: http://www.250bpm.com/blog:16

Using one eventfd per userspace socket still seems a bit wasteful.

Couldn't you use a single pipe for all sockets and write the efd_mask to
the pipe for each socket?

A read from the pipe would behave like epoll_wait.

You might need to use one-shot semantics; but that's probably
the easiest thing in multithreaded apps anyways.
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