From: Mel Gorman <mel@csn.ul.ie>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>,
Linux Memory Management List <linux-mm@kvack.org>,
Pekka Enberg <penberg@cs.helsinki.fi>,
Rik van Riel <riel@redhat.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Nick Piggin <npiggin@suse.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Lin Ming <ming.m.lin@intel.com>,
Zhang Yanmin <yanmin_zhang@linux.intel.com>
Subject: Re: [PATCH 04/20] Convert gfp_zone() to use a table of precalculated value
Date: Mon, 23 Feb 2009 16:40:47 +0000 [thread overview]
Message-ID: <20090223164047.GO6740@csn.ul.ie> (raw)
In-Reply-To: <alpine.DEB.1.10.0902231042440.7790@qirst.com>
On Mon, Feb 23, 2009 at 10:43:20AM -0500, Christoph Lameter wrote:
> On Tue, 24 Feb 2009, Nick Piggin wrote:
>
> > > Are you sure that this is a benefit? Jumps are forward and pretty short
> > > and the compiler is optimizing a branch away in the current code.
> >
> > Pretty easy to mispredict there, though, especially as you can tend
> > to get allocations interleaved between kernel and movable (or simply
> > if the branch predictor is cold there are a lot of branches on x86-64).
> >
> > I would be interested to know if there is a measured improvement.
Not in kernbench at least, but that is no surprise. It's a small
percentage of the overall cost. It'll appear in the noise for anything
other than micro-benchmarks.
> > It
> > adds an extra dcache line to the footprint, but OTOH the instructions
> > you quote is more than one icache line, and presumably Mel's code will
> > be a lot shorter.
>
Yes, it's an index lookup of a shared read-only cache line versus a lot
of code with branches to mispredict. I wasn't happy with the cache line
consumption but it was the first obvious alternative.
> Maybe we can come up with a version of gfp_zone that has no branches and
> no lookup?
>
Ideally, yes, but I didn't spot any obvious way of figuring it out at
compile time then or now. Suggestions?
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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next prev parent reply other threads:[~2009-02-23 16:40 UTC|newest]
Thread overview: 95+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-22 23:17 [RFC PATCH 00/20] Cleanup and optimise the page allocator Mel Gorman
2009-02-22 23:17 ` [PATCH 01/20] Replace __alloc_pages_internal() with __alloc_pages_nodemask() Mel Gorman
2009-02-22 23:17 ` [PATCH 02/20] Do not sanity check order in the fast path Mel Gorman
2009-02-22 23:17 ` [PATCH 03/20] Do not check NUMA node ID when the caller knows the node is valid Mel Gorman
2009-02-23 15:01 ` Christoph Lameter
2009-02-23 16:24 ` Mel Gorman
2009-02-22 23:17 ` [PATCH 04/20] Convert gfp_zone() to use a table of precalculated values Mel Gorman
2009-02-23 11:55 ` [PATCH] mm: clean up __GFP_* flags a bit Peter Zijlstra
2009-02-23 18:01 ` Mel Gorman
2009-02-23 20:27 ` Vegard Nossum
2009-02-23 15:23 ` [PATCH 04/20] Convert gfp_zone() to use a table of precalculated values Christoph Lameter
2009-02-23 15:41 ` Nick Piggin
2009-02-23 15:43 ` [PATCH 04/20] Convert gfp_zone() to use a table of precalculated value Christoph Lameter
2009-02-23 16:40 ` Mel Gorman [this message]
2009-02-23 17:03 ` Christoph Lameter
2009-02-24 1:32 ` KAMEZAWA Hiroyuki
2009-02-24 3:59 ` Nick Piggin
2009-02-24 5:20 ` KAMEZAWA Hiroyuki
2009-02-24 11:36 ` Mel Gorman
2009-02-23 16:33 ` [PATCH 04/20] Convert gfp_zone() to use a table of precalculated values Mel Gorman
2009-02-23 16:33 ` [PATCH 04/20] Convert gfp_zone() to use a table of precalculated value Christoph Lameter
2009-02-23 17:41 ` Mel Gorman
2009-02-22 23:17 ` [PATCH 05/20] Check only once if the zonelist is suitable for the allocation Mel Gorman
2009-02-22 23:17 ` [PATCH 06/20] Break up the allocator entry point into fast and slow paths Mel Gorman
2009-02-22 23:17 ` [PATCH 07/20] Simplify the check on whether cpusets are a factor or not Mel Gorman
2009-02-23 7:14 ` Pekka J Enberg
2009-02-23 9:07 ` Peter Zijlstra
2009-02-23 9:13 ` Pekka Enberg
2009-02-23 11:39 ` Mel Gorman
2009-02-23 13:19 ` Pekka Enberg
2009-02-23 9:14 ` Li Zefan
2009-02-22 23:17 ` [PATCH 08/20] Move check for disabled anti-fragmentation out of fastpath Mel Gorman
2009-02-22 23:17 ` [PATCH 09/20] Calculate the preferred zone for allocation only once Mel Gorman
2009-02-22 23:17 ` [PATCH 10/20] Calculate the migratetype " Mel Gorman
2009-02-22 23:17 ` [PATCH 11/20] Inline get_page_from_freelist() in the fast-path Mel Gorman
2009-02-23 7:21 ` Pekka Enberg
2009-02-23 11:42 ` Mel Gorman
2009-02-23 15:32 ` Nick Piggin
2009-02-24 13:32 ` Mel Gorman
2009-02-24 14:08 ` Nick Piggin
2009-02-24 15:03 ` Mel Gorman
2009-02-22 23:17 ` [PATCH 12/20] Inline __rmqueue_smallest() Mel Gorman
2009-02-22 23:17 ` [PATCH 13/20] Inline buffered_rmqueue() Mel Gorman
2009-02-23 7:24 ` Pekka Enberg
2009-02-23 11:44 ` Mel Gorman
2009-02-22 23:17 ` [PATCH 14/20] Do not call get_pageblock_migratetype() more than necessary Mel Gorman
2009-02-22 23:17 ` [PATCH 15/20] Do not disable interrupts in free_page_mlock() Mel Gorman
2009-02-23 9:19 ` Peter Zijlstra
2009-02-23 12:23 ` Mel Gorman
2009-02-23 12:44 ` Peter Zijlstra
2009-02-23 14:25 ` Mel Gorman
2009-02-22 23:17 ` [PATCH 16/20] Do not setup zonelist cache when there is only one node Mel Gorman
2009-02-22 23:17 ` [PATCH 17/20] Do not double sanity check page attributes during allocation Mel Gorman
2009-02-22 23:17 ` [PATCH 18/20] Split per-cpu list into one-list-per-migrate-type Mel Gorman
2009-02-22 23:17 ` [PATCH 19/20] Batch free pages from migratetype per-cpu lists Mel Gorman
2009-02-22 23:17 ` [PATCH 20/20] Get rid of the concept of hot/cold page freeing Mel Gorman
2009-02-23 9:37 ` Andrew Morton
2009-02-23 23:30 ` Mel Gorman
2009-02-23 23:53 ` Andrew Morton
2009-02-24 11:51 ` Mel Gorman
2009-02-25 0:01 ` Andrew Morton
2009-02-25 16:01 ` Mel Gorman
2009-02-25 16:19 ` Andrew Morton
2009-02-26 16:37 ` Mel Gorman
2009-02-26 17:00 ` Christoph Lameter
2009-02-26 17:15 ` Mel Gorman
2009-02-26 17:30 ` Christoph Lameter
2009-02-27 11:33 ` Nick Piggin
2009-02-27 15:40 ` Christoph Lameter
2009-03-03 13:52 ` Mel Gorman
2009-03-03 18:53 ` Christoph Lameter
2009-02-27 11:38 ` Nick Piggin
2009-03-01 10:37 ` KOSAKI Motohiro
2009-02-25 18:33 ` Christoph Lameter
2009-02-22 23:57 ` [RFC PATCH 00/20] Cleanup and optimise the page allocator Andi Kleen
2009-02-23 12:34 ` Mel Gorman
2009-02-23 15:34 ` [RFC PATCH 00/20] Cleanup and optimise the page allocato Christoph Lameter
2009-02-23 0:02 ` [RFC PATCH 00/20] Cleanup and optimise the page allocator Andi Kleen
2009-02-23 14:32 ` Mel Gorman
2009-02-23 17:49 ` Andi Kleen
2009-02-24 14:32 ` Mel Gorman
2009-02-23 7:29 ` Pekka Enberg
2009-02-23 8:34 ` Zhang, Yanmin
2009-02-23 9:10 ` KOSAKI Motohiro
2009-02-23 11:55 ` [PATCH] mm: gfp_to_alloc_flags() Peter Zijlstra
2009-02-23 14:00 ` Pekka Enberg
2009-02-23 18:17 ` Mel Gorman
2009-02-23 20:09 ` Peter Zijlstra
2009-02-23 22:59 ` Andrew Morton
2009-02-24 8:59 ` Peter Zijlstra
2009-02-23 14:38 ` [RFC PATCH 00/20] Cleanup and optimise the page allocator Christoph Lameter
2009-02-23 14:46 ` Nick Piggin
2009-02-23 15:00 ` Mel Gorman
2009-02-23 15:22 ` Nick Piggin
2009-02-23 20:26 ` Mel Gorman
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