linux-kernel - Re: [RFC][PATCH] fs: optimize inotify/fsnotify code for unwatched files

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Date:	Mon, 22 Jun 2015 11:50:50 -0700
From:	Dave Hansen <dave@...1.net>
To:	paulmck@...ux.vnet.ibm.com, Peter Zijlstra <peterz@...radead.org>
CC:	Andi Kleen <ak@...ux.intel.com>, dave.hansen@...ux.intel.com,
	akpm@...ux-foundation.org, jack@...e.cz, viro@...iv.linux.org.uk,
	eparis@...hat.com, john@...nmccutchan.com, rlove@...ve.org,
	tim.c.chen@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] fs: optimize inotify/fsnotify code for unwatched
 files

On 06/22/2015 08:11 AM, Paul E. McKenney wrote:
> But if Dave is willing to test it, I would be happy to send along
> a fast-readers patch, easy to do.

I'm always willing to test, but the cost of the srcu_read_lock() barrier
shows up even on my 2-year-old "Intel(R) Core(TM) i5-3320M CPU @
2.60GHz" laptop.  The numbers I shared in this thread are on a newer CPU
than that, so I'm fairly confident this will show up on just about any
(big core) Intel CPU newer than SandyBridge.

The tests I've been running are:

	https://github.com/antonblanchard/will-it-scale

with two new 1-byte read/write tests copied in to "tests/":

	https://www.sr71.net/~dave/intel/read1byte.c
	https://www.sr71.net/~dave/intel/write1byte.c

The one-byte thing is silly but it does help isolate the kernel's
overhead from what the app is doing.
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