From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCHSET v4] blk-mq-scheduling framework To: Paolo Valente References: <1481933536-12844-1-git-send-email-axboe@fb.com> <7A8A5078-E9B8-4EBF-BAB1-9E8EEBF3A043@linaro.org> <37570439-97C8-4009-B143-C5E78789A137@linaro.org> <2028A64C-40E5-403D-B5E9-05863E94B4C5@linaro.org> <59b134de-5d2d-5f16-3118-bdc16bc6e36b@fb.com> <22EDFDE7-71FF-4265-8DDE-B141D3FD26B2@linaro.org> <15FC1715-D77C-4E31-811B-60898C0C6DAA@linaro.org> Cc: Jens Axboe , linux-block@vger.kernel.org, Linux-Kernal , Omar Sandoval , Linus Walleij , Ulf Hansson , Mark Brown From: Jens Axboe Message-ID: <0e047692-5ff2-d404-a400-8484e060218b@fb.com> Date: Wed, 25 Jan 2017 09:13:35 -0700 MIME-Version: 1.0 In-Reply-To: <15FC1715-D77C-4E31-811B-60898C0C6DAA@linaro.org> Content-Type: text/plain; charset=windows-1252 List-ID: On 01/25/2017 01:46 AM, Paolo Valente wrote: > >> Il giorno 23 gen 2017, alle ore 18:42, Jens Axboe ha scritto: >> >> On 01/23/2017 10:04 AM, Paolo Valente wrote: >>> >>>> Il giorno 18 gen 2017, alle ore 17:21, Jens Axboe ha scritto: >>>> >>>> On 01/18/2017 08:14 AM, Paolo Valente wrote: >>>>> according to the function blk_mq_sched_put_request, the >>>>> mq.completed_request hook seems to always be invoked (if set) for a >>>>> request for which the mq.put_rq_priv is invoked (if set). >>>> >>>> Correct, any request that came out of blk_mq_sched_get_request() >>>> will always have completed called on it, regardless of whether it >>>> had IO started on it or not. >>>> >>> >>> It seems that some request, after being dispatched, happens to have no >>> mq.put_rq_priv invoked on it now or then. Is it expected? If it is, >>> could you point me to the path through which the end of the life of >>> such a request is handled? >> >> I'm guessing that's a flush request. I added RQF_QUEUED to check for >> that, if RQF_QUEUED is set, you know it has come from your get_request >> handler. >> > > Exactly, the completion-without-put_rq_priv pattern seems to occur > only for requests coming from the flusher, precisely because they have > the flag RQF_ELVPRIV unset. Just to understand: why is this flag > unset for these requests, if they do have private elevator (bfq) > data attached? What am I misunderstanding? > > Just to be certain: this should be the only case where the > completed_request hook is invoked while the put_rq_priv is not, right? They must NOT have scheduler data attached. In your get_request function, you must bypass if blk_mq_sched_bypass_insert() returns true. See how mq-deadline does that. This is important, or you will get hangs with flushes as well, since the IO scheduler private data and the flush data is unionized in the request. -- Jens Axboe