From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D83EFC64EB4 for ; Fri, 30 Nov 2018 22:04:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A3D5E20660 for ; Fri, 30 Nov 2018 22:04:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A3D5E20660 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-block-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726454AbeLAJPL (ORCPT ); Sat, 1 Dec 2018 04:15:11 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57136 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725749AbeLAJPL (ORCPT ); Sat, 1 Dec 2018 04:15:11 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BD305753E2; Fri, 30 Nov 2018 22:04:27 +0000 (UTC) Received: from localhost (unknown [10.18.25.149]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4990F6012E; Fri, 30 Nov 2018 22:04:24 +0000 (UTC) Date: Fri, 30 Nov 2018 17:04:23 -0500 From: Mike Snitzer To: Jens Axboe Cc: Mikulas Patocka , dm-devel@redhat.com, linux-block@vger.kernel.org, "Alasdair G. Kergon" , Christoph Hellwig Subject: Re: [PATCH 2/3] block: switch to per-cpu in-flight counters Message-ID: <20181130220423.GC15049@redhat.com> References: <20181128004250.325095242@debian.vm> <20181130214433.GA15049@redhat.com> <2a7c33ef-0bd0-d901-6a11-cffca1751b9e@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2a7c33ef-0bd0-d901-6a11-cffca1751b9e@kernel.dk> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 30 Nov 2018 22:04:27 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Nov 30 2018 at 4:52pm -0500, Jens Axboe wrote: > On 11/30/18 2:44 PM, Mike Snitzer wrote: > > On Tue, Nov 27 2018 at 7:42pm -0500, > > Mikulas Patocka wrote: > > > >> Now when part_round_stats is gone, we can switch to per-cpu in-flight > >> counters. > >> > >> We use the local-atomic type local_t, so that if part_inc_in_flight or > >> part_dec_in_flight is reentrantly called from an interrupt, the value will > >> be correct. > >> > >> The other counters could be corrupted due to reentrant interrupt, but the > >> corruption only results in slight counter skew - the in_flight counter > >> must be exact, so it needs local_t. > >> > >> Signed-off-by: Mikulas Patocka > >> > >> --- > >> block/bio.c | 4 ++-- > >> block/blk-core.c | 4 ++-- > >> block/blk-merge.c | 2 +- > >> block/genhd.c | 47 +++++++++++++++++++++++++++++++++++------------ > >> drivers/md/dm.c | 4 +--- > >> include/linux/genhd.h | 7 ++++--- > >> 6 files changed, 45 insertions(+), 23 deletions(-) > >> > >> Index: linux-block/block/genhd.c > >> =================================================================== > >> --- linux-block.orig/block/genhd.c 2018-11-28 00:09:59.000000000 +0100 > >> +++ linux-block/block/genhd.c 2018-11-28 00:09:59.000000000 +0100 > >> @@ -45,53 +45,76 @@ static void disk_add_events(struct gendi > >> static void disk_del_events(struct gendisk *disk); > >> static void disk_release_events(struct gendisk *disk); > >> > >> -void part_inc_in_flight(struct request_queue *q, struct hd_struct *part, int rw) > >> +void part_inc_in_flight(struct request_queue *q, int cpu, struct hd_struct *part, int rw) > >> { > >> if (queue_is_mq(q)) > >> return; > >> > >> - atomic_inc(&part->in_flight[rw]); > >> + local_inc(per_cpu_ptr(part->dkstats, cpu)->in_flight); > >> if (part->partno) > >> - atomic_inc(&part_to_disk(part)->part0.in_flight[rw]); > >> + local_inc(per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight); > >> } > >> > >> -void part_dec_in_flight(struct request_queue *q, struct hd_struct *part, int rw) > >> +void part_dec_in_flight(struct request_queue *q, int cpu, struct hd_struct *part, int rw) > >> { > >> if (queue_is_mq(q)) > >> return; > >> > >> - atomic_dec(&part->in_flight[rw]); > >> + local_dec(per_cpu_ptr(part->dkstats, cpu)->in_flight); > >> if (part->partno) > >> - atomic_dec(&part_to_disk(part)->part0.in_flight[rw]); > >> + local_dec(per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight); > >> } > > > > > > The above is wrong, needs this incremental fix: > > Should also be using this_cpu_inc/dec instead. How so? Mikulas is using local_t (original header speaks to why)