From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: [PATCH 2/3] block: switch to per-cpu in-flight counters Date: Fri, 30 Nov 2018 17:04:23 -0500 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-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <2a7c33ef-0bd0-d901-6a11-cffca1751b9e@kernel.dk> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , dm-devel@redhat.com, Mikulas Patocka , "Alasdair G. Kergon" List-Id: dm-devel.ids 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)