From: JeffleXu <jefflexu@linux.alibaba.com> To: Mikulas Patocka <mpatocka@redhat.com> Cc: Mike Snitzer <msnitzer@redhat.com>, Heinz Mauelshagen <heinzm@redhat.com>, axboe@kernel.dk, caspar@linux.alibaba.com, io-uring@vger.kernel.org, linux-block@vger.kernel.org, joseph.qi@linux.alibaba.com, dm-devel@redhat.com, hch@lst.de Subject: Re: [dm-devel] [PATCH 4/4] dm: support I/O polling Date: Thu, 4 Mar 2021 10:57:55 +0800 [thread overview] Message-ID: <f9dd41f1-7a4c-5901-c099-dca08c4e6d65@linux.alibaba.com> (raw) In-Reply-To: <alpine.LRH.2.02.2103030505460.29593@file01.intranet.prod.int.rdu2.redhat.com> On 3/3/21 6:09 PM, Mikulas Patocka wrote: > > > On Wed, 3 Mar 2021, JeffleXu wrote: > >> >> >> On 3/3/21 3:05 AM, Mikulas Patocka wrote: >> >>> Support I/O polling if submit_bio_noacct_mq_direct returned non-empty >>> cookie. >>> >>> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> >>> >>> --- >>> drivers/md/dm.c | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> Index: linux-2.6/drivers/md/dm.c >>> =================================================================== >>> --- linux-2.6.orig/drivers/md/dm.c 2021-03-02 19:26:34.000000000 +0100 >>> +++ linux-2.6/drivers/md/dm.c 2021-03-02 19:26:34.000000000 +0100 >>> @@ -1682,6 +1682,11 @@ static void __split_and_process_bio(stru >>> } >>> } >>> >>> + if (ci.poll_cookie != BLK_QC_T_NONE) { >>> + while (atomic_read(&ci.io->io_count) > 1 && >>> + blk_poll(ci.poll_queue, ci.poll_cookie, true)) ; >>> + } >>> + >>> /* drop the extra reference count */ >>> dec_pending(ci.io, errno_to_blk_status(error)); >>> } >> >> It seems that the general idea of your design is to >> 1) submit *one* split bio >> 2) blk_poll(), waiting the previously submitted split bio complets > > No, I submit all the bios and poll for the last one. > >> and then submit next split bio, repeating the above process. I'm afraid >> the performance may be an issue here, since the batch every time >> blk_poll() reaps may decrease. > > Could you benchmark it? > I will once I finished some other issues. >> Besides, the submitting routine and polling routine is bound together >> here, i.e., polling is always synchronous. > > __split_and_process_bio calls __split_and_process_non_flush in a loop I also noticed that you sent this patch. https://patchwork.kernel.org/project/dm-devel/patch/alpine.LRH.2.02.2103010457510.631@file01.intranet.prod.int.rdu2.redhat.com/ I agree with you that this while() loop here is unnecessary. And thus there's no loop calling __split_and_process_non_flush() in __split_and_process_bio(). > __split_and_process_non_flush records the poll cookie in ci.poll_cookie. > When we processed all the bios, we poll for the last cookie here: > > if (ci.poll_cookie != BLK_QC_T_NONE) { > while (atomic_read(&ci.io->io_count) > 1 && > blk_poll(ci.poll_queue, ci.poll_cookie, true)) ; > } So what will happen if one bio submitted to dm device crosses the device boundary among several target devices (e.g., dm-stripe)? Please refer the following call graph. ``` submit_bio __submit_bio_noacct disk->fops->submit_bio(), calling into __split_and_process_bio(), call __split_and_process_non_flush() once, submitting the *first* split bio disk->fops->submit_bio(), calling into __split_and_process_bio(), call __split_and_process_non_flush() once, submitting the *second* split bio ... ``` So the loop is in __submit_bio_noacct(), rather than __split_and_process_bio(). Your design will send the first split bio, and then poll on this split bio, then send the next split bio, polling on this, go on and on... -- Thanks, Jeffle
WARNING: multiple messages have this Message-ID (diff)
From: JeffleXu <jefflexu@linux.alibaba.com> To: Mikulas Patocka <mpatocka@redhat.com> Cc: axboe@kernel.dk, Mike Snitzer <msnitzer@redhat.com>, Heinz Mauelshagen <heinzm@redhat.com>, caspar@linux.alibaba.com, hch@lst.de, linux-block@vger.kernel.org, joseph.qi@linux.alibaba.com, dm-devel@redhat.com, io-uring@vger.kernel.org Subject: Re: [dm-devel] [PATCH 4/4] dm: support I/O polling Date: Thu, 4 Mar 2021 10:57:55 +0800 [thread overview] Message-ID: <f9dd41f1-7a4c-5901-c099-dca08c4e6d65@linux.alibaba.com> (raw) In-Reply-To: <alpine.LRH.2.02.2103030505460.29593@file01.intranet.prod.int.rdu2.redhat.com> On 3/3/21 6:09 PM, Mikulas Patocka wrote: > > > On Wed, 3 Mar 2021, JeffleXu wrote: > >> >> >> On 3/3/21 3:05 AM, Mikulas Patocka wrote: >> >>> Support I/O polling if submit_bio_noacct_mq_direct returned non-empty >>> cookie. >>> >>> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> >>> >>> --- >>> drivers/md/dm.c | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> Index: linux-2.6/drivers/md/dm.c >>> =================================================================== >>> --- linux-2.6.orig/drivers/md/dm.c 2021-03-02 19:26:34.000000000 +0100 >>> +++ linux-2.6/drivers/md/dm.c 2021-03-02 19:26:34.000000000 +0100 >>> @@ -1682,6 +1682,11 @@ static void __split_and_process_bio(stru >>> } >>> } >>> >>> + if (ci.poll_cookie != BLK_QC_T_NONE) { >>> + while (atomic_read(&ci.io->io_count) > 1 && >>> + blk_poll(ci.poll_queue, ci.poll_cookie, true)) ; >>> + } >>> + >>> /* drop the extra reference count */ >>> dec_pending(ci.io, errno_to_blk_status(error)); >>> } >> >> It seems that the general idea of your design is to >> 1) submit *one* split bio >> 2) blk_poll(), waiting the previously submitted split bio complets > > No, I submit all the bios and poll for the last one. > >> and then submit next split bio, repeating the above process. I'm afraid >> the performance may be an issue here, since the batch every time >> blk_poll() reaps may decrease. > > Could you benchmark it? > I will once I finished some other issues. >> Besides, the submitting routine and polling routine is bound together >> here, i.e., polling is always synchronous. > > __split_and_process_bio calls __split_and_process_non_flush in a loop I also noticed that you sent this patch. https://patchwork.kernel.org/project/dm-devel/patch/alpine.LRH.2.02.2103010457510.631@file01.intranet.prod.int.rdu2.redhat.com/ I agree with you that this while() loop here is unnecessary. And thus there's no loop calling __split_and_process_non_flush() in __split_and_process_bio(). > __split_and_process_non_flush records the poll cookie in ci.poll_cookie. > When we processed all the bios, we poll for the last cookie here: > > if (ci.poll_cookie != BLK_QC_T_NONE) { > while (atomic_read(&ci.io->io_count) > 1 && > blk_poll(ci.poll_queue, ci.poll_cookie, true)) ; > } So what will happen if one bio submitted to dm device crosses the device boundary among several target devices (e.g., dm-stripe)? Please refer the following call graph. ``` submit_bio __submit_bio_noacct disk->fops->submit_bio(), calling into __split_and_process_bio(), call __split_and_process_non_flush() once, submitting the *first* split bio disk->fops->submit_bio(), calling into __split_and_process_bio(), call __split_and_process_non_flush() once, submitting the *second* split bio ... ``` So the loop is in __submit_bio_noacct(), rather than __split_and_process_bio(). Your design will send the first split bio, and then poll on this split bio, then send the next split bio, polling on this, go on and on... -- Thanks, Jeffle -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
next prev parent reply other threads:[~2021-03-04 2:59 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-03-02 19:05 [PATCH 4/4] dm: support I/O polling Mikulas Patocka 2021-03-02 19:05 ` [dm-devel] " Mikulas Patocka 2021-03-03 2:53 ` JeffleXu 2021-03-03 2:53 ` JeffleXu 2021-03-03 10:09 ` Mikulas Patocka 2021-03-03 10:09 ` Mikulas Patocka 2021-03-04 2:57 ` JeffleXu [this message] 2021-03-04 2:57 ` JeffleXu 2021-03-04 10:09 ` Mikulas Patocka 2021-03-04 10:09 ` Mikulas Patocka 2021-03-05 18:21 ` Jens Axboe 2021-03-05 18:21 ` Jens Axboe 2021-03-04 15:01 ` Jeff Moyer 2021-03-04 15:01 ` Jeff Moyer 2021-03-04 15:11 ` Mike Snitzer 2021-03-04 15:11 ` [dm-devel] " Mike Snitzer 2021-03-04 15:12 ` Mikulas Patocka 2021-03-04 15:12 ` Mikulas Patocka 2021-03-05 9:52 ` JeffleXu 2021-03-05 9:52 ` JeffleXu 2021-03-05 17:46 ` Heinz Mauelshagen 2021-03-05 17:46 ` Heinz Mauelshagen 2021-03-05 17:56 ` Heinz Mauelshagen 2021-03-05 17:56 ` Heinz Mauelshagen 2021-03-05 18:09 ` Mike Snitzer 2021-03-05 18:09 ` [dm-devel] " Mike Snitzer 2021-03-05 18:19 ` Heinz Mauelshagen 2021-03-05 18:19 ` Heinz Mauelshagen 2021-03-08 3:54 ` JeffleXu 2021-03-08 3:54 ` JeffleXu 2021-03-08 3:55 ` Jens Axboe 2021-03-08 3:55 ` Jens Axboe 2021-03-09 11:42 ` Heinz Mauelshagen 2021-03-09 11:42 ` Heinz Mauelshagen
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