From: Benjamin LaHaise <bcrl@linux.intel.com>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Andrew Morton <akpm@osdl.org>,
linux-mm@kvack.org, netdev@vger.kernel.org
Subject: Re: [PATCH] avoid atomic op on page free
Date: Mon, 6 Mar 2006 18:10:02 -0800 [thread overview]
Message-ID: <20060307021002.GL32565@linux.intel.com> (raw)
In-Reply-To: <440CEA34.1090205@yahoo.com.au>
On Tue, Mar 07, 2006 at 01:04:36PM +1100, Nick Piggin wrote:
> I'd say it will turn out to be more trouble than its worth, for the
> miserly cost
> avoiding one atomic_inc, and one atomic_dec_and_test on page-local data
> that will
> be in L1 cache. I'd never turn my nose up at anyone just having a go
> though :)
The cost is anything but miserly. Consider that every lock instruction is
a memory barrier which takes your OoO CPU with lots of instructions in flight
to ramp down to just 1 for the time it takes that instruction to execute.
That synchronization is what makes the atomic expensive.
In the case of netperf, I ended up with a 2.5Gbit/s (~30%) performance
improvement through nothing but microoptimizations. There is method to
my madness. ;-)
-ben
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next prev parent reply other threads:[~2006-03-07 2:10 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-03-07 0:10 Benjamin LaHaise
2006-03-07 0:50 ` Andrew Morton
2006-03-07 1:11 ` Benjamin LaHaise
2006-03-07 1:39 ` Andrew Morton
2006-03-07 1:52 ` Benjamin LaHaise
2006-03-07 6:30 ` Andi Kleen
2006-03-07 2:04 ` Nick Piggin
2006-03-07 2:10 ` Benjamin LaHaise [this message]
2006-03-07 4:08 ` Nick Piggin
2006-03-07 2:30 ` Chen, Kenneth W
2006-03-07 4:13 ` Nick Piggin
2006-03-07 1:21 ` Rick Jones
2006-03-07 1:53 ` Nick Piggin
2006-03-07 1:58 ` Benjamin LaHaise
2006-03-07 2:14 ` Nick Piggin
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