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

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Date:	Sat, 9 Feb 2013 11:51:49 +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 09/02/13 04:54, Eric Wong wrote:
> >>>Using one eventfd per userspace socket still seems a bit wasteful.
> >>
> >>Wasteful in what sense? Occupying a slot in file descriptor table?
> >>That's the price for having the socket uniquely identified by the
> >>fd.
> >
> >Yes.  I realize eventfd is small, but I don't think eventfd is needed
> >at all, here.  Just one pipe.
> 
> Ah. Got you! You mean not to change the kernel, just use pipe for
> the purpose.
> 
> However, the convoluted pipe-style design is the problem I am trying
> to solve rather than the solution. It leads to convoluted APIs with
> convoluted semantics as described in the article. I've been using
> that kind of design for past 8 years and every time I have to deal
> with it I swear that one day I will implement a proper in-kernel
> solution to get rid of the hack.
> 
> And now I have finally done so.

Yes, your eventfd change is probably the best way if you want/need
to only watch a subset of your sockets, especially if you want
poll/select to be an option.

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