linux-kernel - Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out

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Message-ID: <1317938915.4729.31.camel@gandalf.stny.rr.com>
Date:	Thu, 06 Oct 2011 18:08:34 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Jason Baron <jbaron@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	David Daney <david.daney@...ium.com>,
	Michael Ellerman <michael@...erman.id.au>,
	Jan Glauber <jang@...ux.vnet.ibm.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	peterz@...radead.org, rth@...hat.com
Subject: Re: [PATCH RFC V2 3/5] jump_label: if a key has already been
 initialized, don't nop it out

On Thu, 2011-10-06 at 14:39 -0700, Jeremy Fitzhardinge wrote:

> I'm not sure it would be a win, necessarily.  My test with back-to-back
> jmp2 was definitely slower than with the nop padding it out to 5 bytes;
> I suspect that's a result of having too many jmps within one cacheline. 
> Of course, there's no reason why the CPU would optimise for jumps to
> jumps, so perhaps its just hitting a "stupid programmer" path.

Just a note. Micro-benchmarks are known to be as good as political polls
and statistics. They show a much different view of the world than what
is really there.

-- Steve


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