From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753188Ab3F1Tb4 (ORCPT ); Fri, 28 Jun 2013 15:31:56 -0400 Received: from merlin.infradead.org ([205.233.59.134]:58969 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752824Ab3F1Tbz (ORCPT ); Fri, 28 Jun 2013 15:31:55 -0400 Date: Fri, 28 Jun 2013 21:31:52 +0200 From: Jens Axboe To: Jan Kara Cc: LKML Subject: Re: [PATCH] block: Reserve only one queue tag for sync IO if only 3 tags are available Message-ID: <20130628193152.GF24293@kernel.dk> References: <1372432127-9716-1-git-send-email-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1372432127-9716-1-git-send-email-jack@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 28 2013, Jan Kara wrote: > In case a device has three tags available we still reserve two of them > for sync IO. That leaves only a single tag for async IO such as > writeback from flusher thread which results in poor performance. > > Allow async IO to consume two tags in case queue has three tag availabe > to get a decent async write performance. > > This patch improves streaming write performance on a machine with such disk > from ~21 MB/s to ~52 MB/s. Also postmark throughput in presence of > streaming writer improves from 8 to 12 transactions per second so sync > IO doesn't seem to be harmed in presence of heavy async writer. That's pretty crazy! Never seen a device like that. But yes, it obviously exists, and the 2 reserved tags doesn't work well for that. So it's an improvement. Thanks, will queue up for 3.11. -- Jens Axboe