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 16:44:33 -0500 Message-ID: <20181130214433.GA15049@redhat.com> References: <20181128004250.325095242@debian.vm> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20181128004250.325095242@debian.vm> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mikulas Patocka Cc: Jens Axboe , linux-block@vger.kernel.org, dm-devel@redhat.com, "Alasdair G. Kergon" , Christoph Hellwig List-Id: dm-devel.ids 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: diff --git a/block/genhd.c b/block/genhd.c index 2ed431098953..3397288a2926 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -50,9 +50,9 @@ void part_inc_in_flight(struct request_queue *q, int cpu, struct hd_struct *part if (queue_is_mq(q)) return; - local_inc(per_cpu_ptr(part->dkstats, cpu)->in_flight); + local_inc(&per_cpu_ptr(part->dkstats, cpu)->in_flight[rw]); if (part->partno) - local_inc(per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight); + local_inc(&per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight[rw]); } void part_dec_in_flight(struct request_queue *q, int cpu, struct hd_struct *part, int rw) @@ -60,9 +60,9 @@ void part_dec_in_flight(struct request_queue *q, int cpu, struct hd_struct *part if (queue_is_mq(q)) return; - local_dec(per_cpu_ptr(part->dkstats, cpu)->in_flight); + local_dec(&per_cpu_ptr(part->dkstats, cpu)->in_flight[rw]); if (part->partno) - local_dec(per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight); + local_dec(&per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight[rw]); } unsigned int part_in_flight(struct request_queue *q, struct hd_struct *part)