From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 11 Mar 2004 10:55:27 -0800 From: Andrew Morton Subject: Re: blk_congestion_wait racy? Message-Id: <20040311105527.0de6b69a.akpm@osdl.org> In-Reply-To: References: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Martin Schwidefsky Cc: piggin@cyberone.com.au, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Martin Schwidefsky wrote: > > > Martin, have you tried adding this printk? > > Sorry for the delay. I had to get 2.6.4-mm1 working before doing the > "ouch" test. The new pte_to_pgprot/pgoff_prot_to_pte stuff wasn't easy. Yes, sorry, all the world's an x86 :( Could you please send me whatever diffs were needed to get it all going? There are porting instructions in ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.4/2.6.4-mm1/broken-out/remap-file-pages-prot-2.6.4-rc1-mm1-A1.patch but maybe it's a bit late for that. > I tested 2.6.4-mm1 with the blk_run_queues move and the ouch printk. > The first interesting observation is that 2.6.4-mm1 behaves MUCH better > then 2.6.4: > > 2.6.4-mm1 with 1 cpu > # time ./mempig 600 > Count (1Meg blocks) = 600 > 600 of 600 > Done. > > real 0m2.587s > user 0m0.100s > sys 0m0.730s > # I thought you were running a 256MB machine? Two seconds for 400 megs of swapout? What's up? > 2.6.4-mm1 with 2 cpus > # time ./mempig 600 > Count (1Meg blocks) = 600 > 600 of 600 > Done. > > real 0m10.313s > user 0m0.160s > sys 0m0.780s > # > > 2.6.4 takes > 1min for the test with 2 cpus. > > The second observation is that I get only a few "ouch" messages. They > all come from the blk_congestion_wait in try_to_free_pages, as expected. > What I did not expect is that I only got 9 "ouches" for the run with > 2 cpus. An ouch-per-second sounds reasonable. It could simply be that the CPUs were off running other tasks - those timeout are less than scheduling quanta. The 4x performance difference remains not understood. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org