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[68.160.176.52]) by smtp.gmail.com with ESMTPSA id m64sm5145000qkb.90.2021.01.08.09.33.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Jan 2021 09:33:21 -0800 (PST) Sender: Mike Snitzer Date: Fri, 8 Jan 2021 12:33:20 -0500 From: Mike Snitzer To: JeffleXu Cc: linux-block@vger.kernel.org, dm-devel@redhat.com, io-uring@vger.kernel.org Subject: Re: [PATCH RFC 3/7] block: add iopoll method for non-mq device Message-ID: <20210108173320.GA6584@lobo> References: <20201223112624.78955-1-jefflexu@linux.alibaba.com> <20201223112624.78955-4-jefflexu@linux.alibaba.com> <20210107214758.GC21239@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, Jan 07 2021 at 10:24pm -0500, JeffleXu wrote: > > > On 1/8/21 5:47 AM, Mike Snitzer wrote: > > On Wed, Dec 23 2020 at 6:26am -0500, > > Jeffle Xu wrote: > > > >> ->poll_fn is introduced in commit ea435e1b9392 ("block: add a poll_fn > >> callback to struct request_queue") for supporting non-mq queues such as > >> nvme multipath, but removed in commit 529262d56dbe ("block: remove > >> ->poll_fn"). > >> > >> To add support of IO polling for non-mq device, this method need to be > >> back. Since commit c62b37d96b6e ("block: move ->make_request_fn to > >> struct block_device_operations") has moved all callbacks into struct > >> block_device_operations in gendisk, we also add the new method named > >> ->iopoll in block_device_operations. > > > > Please update patch subject and header to: > > > > block: add iopoll method to support bio-based IO polling > > > > ->poll_fn was introduced in commit ea435e1b9392 ("block: add a poll_fn > > callback to struct request_queue") to support bio-based queues such as > > nvme multipath, but was later removed in commit 529262d56dbe ("block: > > remove ->poll_fn"). > > > > Given commit c62b37d96b6e ("block: move ->make_request_fn to struct > > block_device_operations") restore the possibility of bio-based IO > > polling support by adding an ->iopoll method to gendisk->fops. > > Elevate bulk of blk_mq_poll() implementation to blk_poll() and reduce > > blk_mq_poll() to blk-mq specific code that is called from blk_poll(). > > > >> Signed-off-by: Jeffle Xu > >> --- > >> block/blk-core.c | 79 ++++++++++++++++++++++++++++++++++++++++++ > >> block/blk-mq.c | 70 +++++-------------------------------- > >> include/linux/blk-mq.h | 3 ++ > >> include/linux/blkdev.h | 1 + > >> 4 files changed, 92 insertions(+), 61 deletions(-) > >> > >> diff --git a/block/blk-core.c b/block/blk-core.c > >> index 96e5fcd7f071..2f5c51ce32e3 100644 > >> --- a/block/blk-core.c > >> +++ b/block/blk-core.c > >> @@ -1131,6 +1131,85 @@ blk_qc_t submit_bio(struct bio *bio) > >> } > >> EXPORT_SYMBOL(submit_bio); > >> > >> +static bool blk_poll_hybrid(struct request_queue *q, blk_qc_t cookie) > >> +{ > >> + struct blk_mq_hw_ctx *hctx; > >> + > >> + /* TODO: bio-based device doesn't support hybrid poll. */ > >> + if (!queue_is_mq(q)) > >> + return false; > >> + > >> + hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)]; > >> + if (blk_mq_poll_hybrid(q, hctx, cookie)) > >> + return true; > >> + > >> + hctx->poll_considered++; > >> + return false; > >> +} > > > > I don't see where you ever backfill bio-based hybrid support (in > > the following patches in this series, so it is lingering TODO). > > Yes the hybrid polling is not implemented and thus bypassed for > bio-based device currently. > > > > >> + > >> +/** > >> + * blk_poll - poll for IO completions > >> + * @q: the queue > >> + * @cookie: cookie passed back at IO submission time > >> + * @spin: whether to spin for completions > >> + * > >> + * Description: > >> + * Poll for completions on the passed in queue. Returns number of > >> + * completed entries found. If @spin is true, then blk_poll will continue > >> + * looping until at least one completion is found, unless the task is > >> + * otherwise marked running (or we need to reschedule). > >> + */ > >> +int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin) > >> +{ > >> + long state; > >> + > >> + if (!blk_qc_t_valid(cookie) || > >> + !test_bit(QUEUE_FLAG_POLL, &q->queue_flags)) > >> + return 0; > >> + > >> + if (current->plug) > >> + blk_flush_plug_list(current->plug, false); > >> + > >> + /* > >> + * If we sleep, have the caller restart the poll loop to reset > >> + * the state. Like for the other success return cases, the > >> + * caller is responsible for checking if the IO completed. If > >> + * the IO isn't complete, we'll get called again and will go > >> + * straight to the busy poll loop. If specified not to spin, > >> + * we also should not sleep. > >> + */ > >> + if (spin && blk_poll_hybrid(q, cookie)) > >> + return 1; > >> + > >> + state = current->state; > >> + do { > >> + int ret; > >> + struct gendisk *disk = queue_to_disk(q); > >> + > >> + if (disk->fops->iopoll) > >> + ret = disk->fops->iopoll(q, cookie); > >> + else > >> + ret = blk_mq_poll(q, cookie); > > The original code is indeed buggy. For bio-based device, ->iopoll() may > not be implemented while QUEUE_FLAG_POLL flag is still set, in which > case blk_mq_poll() will be called for this bio-based device. Yes, here is the patch I created to capture my suggestions. Provided it looks good to you, please fold it into patch 3 when you rebase for posting a v2 of your patchset: From: Mike Snitzer Date: Thu, 7 Jan 2021 20:45:17 -0500 Subject: [PATCH] fixup patch 3 --- block/blk-core.c | 51 +++++++++++++++++++++----------------------------- block/blk-mq.c | 6 ++---- include/linux/blk-mq.h | 3 ++- 3 files changed, 25 insertions(+), 35 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index e6671f6ce1a4..44f62dc0fa9f 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1212,22 +1212,6 @@ int blk_bio_poll(struct request_queue *q, blk_qc_t cookie) } EXPORT_SYMBOL(blk_bio_poll); -static bool blk_poll_hybrid(struct request_queue *q, blk_qc_t cookie) -{ - struct blk_mq_hw_ctx *hctx; - - /* TODO: bio-based device doesn't support hybrid poll. */ - if (!queue_is_mq(q)) - return false; - - hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)]; - if (blk_mq_poll_hybrid(q, hctx, cookie)) - return true; - - hctx->poll_considered++; - return false; -} - /** * blk_poll - poll for IO completions * @q: the queue @@ -1243,6 +1227,8 @@ static bool blk_poll_hybrid(struct request_queue *q, blk_qc_t cookie) int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin) { long state; + struct blk_mq_hw_ctx *hctx = NULL; + struct gendisk *disk = NULL; if (!blk_qc_t_valid(cookie) || !test_bit(QUEUE_FLAG_POLL, &q->queue_flags)) @@ -1251,26 +1237,31 @@ int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin) if (current->plug) blk_flush_plug_list(current->plug, false); - /* - * If we sleep, have the caller restart the poll loop to reset - * the state. Like for the other success return cases, the - * caller is responsible for checking if the IO completed. If - * the IO isn't complete, we'll get called again and will go - * straight to the busy poll loop. If specified not to spin, - * we also should not sleep. - */ - if (spin && blk_poll_hybrid(q, cookie)) - return 1; + if (queue_is_mq(q)) { + /* + * If we sleep, have the caller restart the poll loop to reset + * the state. Like for the other success return cases, the + * caller is responsible for checking if the IO completed. If + * the IO isn't complete, we'll get called again and will go + * straight to the busy poll loop. If specified not to spin, + * we also should not sleep. + */ + hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)]; + if (spin && blk_mq_poll_hybrid(q, hctx, cookie)) + return 1; + hctx->poll_considered++; + } else + disk = queue_to_disk(q); state = current->state; do { int ret; - struct gendisk *disk = queue_to_disk(q); - if (disk->fops->iopoll) + if (hctx) + ret = blk_mq_poll(q, hctx, cookie); + else if (disk->fops->iopoll) ret = disk->fops->iopoll(q, cookie); - else - ret = blk_mq_poll(q, cookie); + if (ret > 0) { __set_current_state(TASK_RUNNING); return ret; diff --git a/block/blk-mq.c b/block/blk-mq.c index fcb44604f806..90d8dead1da5 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3826,12 +3826,10 @@ bool blk_mq_poll_hybrid(struct request_queue *q, return blk_mq_poll_hybrid_sleep(q, rq); } -int blk_mq_poll(struct request_queue *q, blk_qc_t cookie) +int blk_mq_poll(struct request_queue *q, + struct blk_mq_hw_ctx *hctx, blk_qc_t cookie) { int ret; - struct blk_mq_hw_ctx *hctx; - - hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)]; hctx->poll_invoked++; ret = q->mq_ops->poll(hctx); diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 2f3742207df5..b95f2ffa866f 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -607,7 +607,8 @@ static inline void blk_rq_bio_prep(struct request *rq, struct bio *bio, } blk_qc_t blk_mq_submit_bio(struct bio *bio); -int blk_mq_poll(struct request_queue *q, blk_qc_t cookie); +int blk_mq_poll(struct request_queue *q, + struct blk_mq_hw_ctx *hctx, blk_qc_t cookie); bool blk_mq_poll_hybrid(struct request_queue *q, struct blk_mq_hw_ctx *hctx, blk_qc_t cookie); void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx, -- 2.15.0