Messages in this thread | | | Subject | Re: [PATCH RFT] blk-mq: optimize queue tag busy iter for shared_tags | From | John Garry <> | Date | Tue, 21 Dec 2021 12:55:44 +0000 |
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On 21/12/2021 12:31, Kashyap Desai wrote:
Hi Kashyap,
What kernel is this for? 5.17 or 5.16 + stable? Your intention is not clear to me.
> In [0], CPU usage for blk_mq_queue_tag_busy_iter() was optimized, but > there are still periodic call of blk_mq_queue_tag_busy_iter() from > below context. Below context is used for block layer timer to find out > potential expired command (per request queue) which requires tag iteration > almost every 5 seconds(defined BLK_MAX_TIMEOUT) for each request queue. > > kthread > worker_thread > process_one_work > blk_mq_timeout_work > blk_mq_queue_tag_busy_iter > bt_iter > blk_mq_find_and_get_req > _raw_spin_lock_irqsave > native_queued_spin_lock_slowpath > > Changes in this patch optimize extra iterations of tags in case of > shared_tags. One iteration of shared_tags can give expected results for > iterate function. > > Setup - AMD64 Gen-4.0 Server. > 64 Virtual Drive created using 16 Nvme drives + mpi3mr driver (in > shared_tags mode) > > Test command - > fio 64.fio --rw=randread --bs=4K --iodepth=32 --numjobs=2 --ioscheduler=mq-deadline --disk_util=0 > > Without this patch on 5.16.0-rc5, mpi3mr driver in shared_tags mode can > give 4.0M IOPs vs expected to get ~6.0M. > Snippet of perf top > > 25.42% [kernel] [k] native_queued_spin_lock_slowpath > 3.95% [kernel] [k] cpupri_set > 2.05% [kernel] [k] __blk_mq_get_driver_tag > 1.67% [kernel] [k] __rcu_read_unlock > 1.63% [kernel] [k] check_preemption_disabled > > After applying this patch on 5.16.0-rc5, mpi3mr driver in shared_tags > mode reach up to 5.8M IOPs. > > Snippet of perf top > > 7.95% [kernel] [k] native_queued_spin_lock_slowpath > 5.61% [kernel] [k] cpupri_set > 2.98% [kernel] [k] acpi_processor_ffh_cstate_enter > 2.49% [kernel] [k] read_tsc > 2.15% [kernel] [k] check_preemption_disabled > > > [0] https://lore.kernel.org/all/9b092ca49e9b5415772cd950a3c12584@mail.gmail.com/ > > > Cc: linux-block@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: john.garry@huawei.com > Cc: ming.lei@redhat.com > Cc: sathya.prakash@broadcom.com > Signed-off-by: Kashyap Desai <kashyap.desai@broadcom.com> > --- > block/blk-mq-tag.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index 995336abee33..3e0a8e79f966 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -253,7 +253,8 @@ static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data) > if (!rq) > return true; > > - if (rq->q == hctx->queue && rq->mq_hctx == hctx) > + if (rq->q == hctx->queue && (rq->mq_hctx == hctx || > + blk_mq_is_shared_tags(hctx->flags))) > ret = iter_data->fn(hctx, rq, iter_data->data, reserved); > blk_mq_put_rq_ref(rq); > return ret; > @@ -484,6 +485,14 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, > if (tags->nr_reserved_tags) > bt_for_each(hctx, &tags->breserved_tags, fn, priv, true); > bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false); > + > + /* In case of shared bitmap if shared_tags is allocated, it is not required > + * to iterate all the hctx. Looping one hctx is good enough. > + */ > + if (blk_mq_is_shared_tags(hctx->flags)) { > + blk_queue_exit(q); > + return;
this looks like v5.16-rc6 code
> + } > } > blk_queue_exit(q); > } >
Thanks, John
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