Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752044AbaFECdp (ORCPT ); Wed, 4 Jun 2014 22:33:45 -0400 Received: from mail-ie0-f172.google.com ([209.85.223.172]:56768 "EHLO mail-ie0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751339AbaFECdn (ORCPT ); Wed, 4 Jun 2014 22:33:43 -0400 Date: Thu, 5 Jun 2014 10:33:34 +0800 From: Shaohua Li To: Jens Axboe Cc: Matias =?iso-8859-1?Q?Bj=F8rling?= , "Sam Bradshaw (sbradshaw)" , LKML Subject: Re: [PATCH] block: per-cpu counters for in-flight IO accounting Message-ID: <20140605023334.GB22826@kernel.org> References: <1399627061-5960-2-git-send-email-m@bjorling.me> <536CE25C.5040107@kernel.dk> <536D0537.7010905@kernel.dk> <20140530121119.GA1637@kernel.org> <53888C80.2020206@kernel.dk> <20140604103901.GA14383@kernel.org> <538F7CCE.3050508@kernel.dk> <20140605020934.GB13953@kernel.org> <538FD300.7010706@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <538FD300.7010706@kernel.dk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 04, 2014 at 08:16:32PM -0600, Jens Axboe wrote: > On 2014-06-04 20:09, Shaohua Li wrote: > >On Wed, Jun 04, 2014 at 02:08:46PM -0600, Jens Axboe wrote: > >>On 06/04/2014 05:29 AM, Matias Bj?rling wrote: > >>>It's in > >>> > >>>blk_io_account_start > >>> part_round_stats > >>> part_round_state_single > >>> part_in_flight > >>> > >>>I like the granularity idea. > >> > >>And similarly from blk_io_account_done() - which makes it even worse, > >>since it at both ends of the IO chain. > > > >But part_round_state_single is supposed to only call part_in_flight every > >jiffery. Maybe we need something below: > >1. set part->stamp immediately > >2. fixed granularity > >Untested though. > > > > > >diff --git a/block/blk-core.c b/block/blk-core.c > >index 40d6548..5f0acaa 100644 > >--- a/block/blk-core.c > >+++ b/block/blk-core.c > >@@ -1270,17 +1270,19 @@ static void part_round_stats_single(int cpu, struct hd_struct *part, > > unsigned long now) > > { > > int inflight; > >+ unsigned long old_stamp; > > > >- if (now == part->stamp) > >+ if (time_before(now, part->stamp + msecs_to_jiffies(10))) > > return; > >+ old_stamp = part->stamp; > >+ part->stamp = now; > > > > inflight = part_in_flight(part); > > if (inflight) { > > __part_stat_add(cpu, part, time_in_queue, > >- inflight * (now - part->stamp)); > >- __part_stat_add(cpu, part, io_ticks, (now - part->stamp)); > >+ inflight * (now - old_stamp)); > >+ __part_stat_add(cpu, part, io_ticks, (now - old_stamp)); > > } > >- part->stamp = now; > > } > > > > /** > > It'd be a good improvement, and one we should be able to do without > screwing anything up. It'd be identical to anyone running at HZ==100 > right now. > > So the above we can easily do, and arguably should just do. We wont > see real scaling in the IO stats path before we fixup the hd_struct > referencing as well, however. That's true. maybe a percpu_ref works here. Thanks, Shaohua -- 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/