Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755145Ab1EEPUv (ORCPT ); Thu, 5 May 2011 11:20:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45224 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754067Ab1EEPUu (ORCPT ); Thu, 5 May 2011 11:20:50 -0400 Date: Thu, 5 May 2011 17:20:40 +0200 (CEST) From: Lukas Czerner X-X-Sender: lukas@dhcp-27-109.brq.redhat.com To: Jens Axboe cc: Lukas Czerner , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Dmitry Monakhov , Jeff Moyer Subject: Re: [PATCH 1/3] blkdev: Submit discard bio in batches in blkdev_issue_discard() In-Reply-To: <4DBEDA78.7020502@fusionio.com> Message-ID: References: <1304345841-20063-1-git-send-email-lczerner@redhat.com> <4DBEDA78.7020502@fusionio.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2081 Lines: 50 On Mon, 2 May 2011, Jens Axboe wrote: > On 2011-05-02 08:17, Lukas Czerner wrote: > > Currently we are waiting for every submitted REQ_DISCARD bio separately, > > but it can have unwanted consequences of repeatedly flushing the queue, > > so we rather submit bios in batches and wait for the entire batch, hence > > narrowing the window of other ios going in. > > > > Use bio_batch_end_io() and struct bio_batch for that purpose, the same > > is used by blkdev_issue_zeroout(). Also change bio_batch_end_io() so we > > always set !BIO_UPTODATE in the case of error and remove the check for > > bb, since we are the only user of this function and we always set this. > > > > Remove bio_get()/bio_put() from the blkdev_issue_discard() since > > bio_alloc() and bio_batch_end_io() is doing the same thing, hence it is > > not needed anymore. > > > > I have done simple dd testing with surprising results. The script I have > > used is: > > > > for i in $(seq 10); do > > echo $i > > dd if=/dev/sdb1 of=/dev/sdc1 bs=4k & > > sleep 5 > > done > > /usr/bin/time -f %e ./blkdiscard /dev/sdc1 > > > > Running time of BLKDISCARD on the whole device: > > with patch without patch > > 0.95 15.58 > > > > So we can see that in this artificial test the kernel with the patch > > applied is approx 16x faster in discarding the device. > > Good results. It'd be more efficient to add the vectored discard support > and use it for this too though, and it would get rid of the need to wait > on the batches since there'd be just one discard bio for the ranges. > Since we do not have vectored discard yet, can this change go in as it is ? Also, Christoph thinks that it would not help anyway since the we do batch the discard requests only when it exceeds the max range. Thanks! -Lukas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/