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Fri, 5 Mar 2021 18:19:26 +0000 (UTC) Received: from [192.168.1.10] (ovpn-114-106.ams2.redhat.com [10.36.114.106]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BF3AD19CB0; Fri, 5 Mar 2021 18:19:23 +0000 (UTC) Subject: Re: [dm-devel] [PATCH 4/4] dm: support I/O polling To: Mike Snitzer Cc: 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, Mikulas Patocka , JeffleXu , hch@lst.de References: <20210302190555.201228400@debian-a64.vm> <33fa121a-88a8-5c27-0a43-a7efc9b5b3e3@linux.alibaba.com> <157a750d-3d58-ae2e-07f1-b677c1b471c7@linux.alibaba.com> <20210305180938.GA21127@redhat.com> From: Heinz Mauelshagen Message-ID: Date: Fri, 5 Mar 2021 19:19:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210305180938.GA21127@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 3/5/21 7:09 PM, Mike Snitzer wrote: > On Fri, Mar 05 2021 at 12:56pm -0500, > Heinz Mauelshagen wrote: > >> On 3/5/21 6:46 PM, Heinz Mauelshagen wrote: >>> On 3/5/21 10:52 AM, JeffleXu wrote: >>>> 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 >>>>>>> >>>>>>> --- >>>>>>>   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 only tested dm-linear. >>>> >>>> The configuration (dm table) of dm-linear is: >>>> 0 1048576 linear /dev/nvme0n1 0 >>>> 1048576 1048576 linear /dev/nvme2n1 0 >>>> 2097152 1048576 linear /dev/nvme5n1 0 >>>> >>>> >>>> fio script used is: >>>> ``` >>>> $cat fio.conf >>>> [global] >>>> name=iouring-sqpoll-iopoll-1 >>>> ioengine=io_uring >>>> iodepth=128 >>>> numjobs=1 >>>> thread >>>> rw=randread >>>> direct=1 >>>> registerfiles=1 >>>> hipri=1 >>>> runtime=10 >>>> time_based >>>> group_reporting >>>> randrepeat=0 >>>> filename=/dev/mapper/testdev >>>> bs=4k >>>> >>>> [job-1] >>>> cpus_allowed=14 >>>> ``` >>>> >>>> IOPS (IRQ mode) | IOPS (iopoll mode (hipri=1)) >>>> --------------- | -------------------- >>>>             213k |           19k >>>> >>>> At least, it doesn't work well with io_uring interface. >>>> >>>> >>> >>> Jeffle, >>> >>> I ran your above fio test on a linear LV split across 3 NVMes to >>> second your split mapping >>> (system: 32 core Intel, 256GiB RAM) comparing io engines sync, >>> libaio and io_uring, >>> the latter w/ and w/o hipri (sync+libaio obviously w/o >>> registerfiles and hipri) which resulted ok: >>> >>> >>> >>> sync  |  libaio  |  IRQ mode (hipri=0) | iopoll (hipri=1) >>> ------|----------|---------------------|----------------- 56.3K >>> |    290K  |                329K |             351K I can't second >>> your drastic hipri=1 drop here... >> >> Sorry, email mess. >> >> >> sync   |  libaio  |  IRQ mode (hipri=0) | iopoll (hipri=1) >> -------|----------|---------------------|----------------- >> 56.3K  |    290K  |                329K |             351K >> >> >> >> I can't second your drastic hipri=1 drop here... > I think your result is just showcasing your powerful system's ability to > poll every related HW queue.. whereas Jeffle's system is likely somehow > more constrained (on a cpu level, memory, whatever). Jeffle, mind explaining your test system configuration a bit more (cores, ram, i/o config to your NVMes) so that we have a better base for such assumption? Thanks, Heinz > > My basis for this is that Mikulas' changes simply always return an > invalid cookie (BLK_QC_T_NONE) for purposes of intelligent IO polling. > > Such an implementation is completely invalid. > > I discussed with Jens and he said: > "it needs to return something that f_op->iopoll() can make sense of. > otherwise you have no option but to try everything." > > Mike > > -- > dm-devel mailing list > dm-devel@redhat.com > https://listman.redhat.com/mailman/listinfo/dm-devel