linux-kernel - Re: [PATCH] epoll: trim epitem by one cache line on x86

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Message-Id: <20130308155410.3c63f24ee28e6532006cb0d4@linux-foundation.org>
Date:	Fri, 8 Mar 2013 15:54:10 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric Wong <normalperson@...t.net>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] epoll: trim epitem by one cache line on x86_64

On Thu, 7 Mar 2013 10:32:40 +0000 Eric Wong <normalperson@...t.net> wrote:

> Andrew Morton <akpm@...ux-foundation.org> wrote:
> > It's going to be hard to maintain this - someone will change something
> > sometime and break it.  I suppose we could add a runtime check if we
> > cared enough.  Adding a big fat comment to struct epitem might help.
> 
> Thanks for looking at this patch.  I'll send a patch with a comment
> about keeping epitem size in check.  Also, would adding (with comments):
> 
> 	BUILD_BUG_ON(sizeof(struct epitem) > 128);
> 
> ...be too heavy-handed?  I used that in my testing.  I'll check for:
> sizeof(void *) <= 8 too; in case 128-bit machines appear...

I guess such a check might avoid accidents in the future.  If it
becomes a problem, we can always delete it.

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