From: Paolo Valente <paolo.valente@linaro.org> To: "Michal Koutný" <mkoutny@suse.com> Cc: Tejun Heo <tj@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, clm@fb.com, dennisz@fb.com, Josef Bacik <jbacik@fb.com>, kernel-team@fb.com, newella@fb.com, lizefan@huawei.com, axboe@kernel.dk, Rik van Riel <riel@surriel.com>, josef@toxicpanda.com, cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 08/10] blkcg: implement blk-iocost Date: Fri, 1 Nov 2019 17:56:48 +0100 [thread overview] Message-ID: <F45F2906-AB10-473D-B515-793E8FB10E6A@linaro.org> (raw) In-Reply-To: <20191101161506.GA28212@blackbody.suse.cz> > Il giorno 1 nov 2019, alle ore 17:15, Michal Koutný <mkoutny@suse.com> ha scritto: > > Hello > Hi Michal, > (I realize it's likely late for the remark but I'd like to bring it up > anyway.) > > On Mon, Oct 14, 2019 at 08:36:43AM -0700, Tejun Heo <tj@kernel.org> wrote: >> We likely can talk on the subject >> for a really long time probalby because there's no clearly technically >> better choice here, so... > I agree with you that functionally the two options are equal and also > from configuration POV they seem both sensible. > > I checked where BFQ stores its per-device parameters and its under the > sysfs directory of given device's iosched directory. So from the user > perspective it'd be more consistent if all similar tunables resided > under that location. > > (OTOH, I admit I'm not that familiar with block layer internals to > identify the overlap between IO scheduler and IO controller.) > If useful for you to know, BFQ parameters are not meant to changed (apart from the low_latency tunable, if one wants full control on weights). Parameters are a testing aid, to use in case of an anomaly. After solving the anomaly, default values should be used again. Thanks, Paolo >> Yeah, it's kinda unfortunate that it requires this many parameters but >> at least my opinion is that that's reflecting the inherent >> complexities of the underlying devices and how workloads interact with >> them. > After I learnt about the existence of BFQ tunables, I'm no longer > concerned by the complexity of the parameter space. > > Thanks for the explanations of QoS purpose. > >> For QoS parameters, Andy is currently working on a method to determine >> the set of parametesr which are at the edge of total work cliff - >> ie. the point where tighetning QoS params further starts reducing the >> total amount of work the device can do significantly. > The QoS description in the Documentation/ describes the interpretation > of the individual parameters, however, this purpose and how it works was > not clear to be from that. I think the QoS policy would deserve similar > description in the Documentation/. > >> Nothing can issue IOs indefinitely without some of them completing and >> the total amount of work a workload can do is conjoined with the >> completion latencies. [...] > I may reply to this point later. However, if that provably works, I'm > likely missing something in my understanding, so that'd be irrelevant. > > Cheers, > Michal
next prev parent reply other threads:[~2019-11-01 16:56 UTC|newest] Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-08-28 22:05 [PATCHSET v3 block/for-linus] IO cost model based work-conserving porportional controller Tejun Heo 2019-08-28 22:05 ` [PATCH 01/10] blkcg: pass @q and @blkcg into blkcg_pol_alloc_pd_fn() Tejun Heo 2019-08-28 22:05 ` [PATCH 02/10] blkcg: make ->cpd_init_fn() optional Tejun Heo 2019-08-28 22:05 ` [PATCH 03/10] blkcg: separate blkcg_conf_get_disk() out of blkg_conf_prep() Tejun Heo 2019-08-28 22:05 ` [PATCH 04/10] block/rq_qos: add rq_qos_merge() Tejun Heo 2019-08-28 22:05 ` [PATCH 05/10] block/rq_qos: implement rq_qos_ops->queue_depth_changed() Tejun Heo 2019-08-28 22:05 ` [PATCH 06/10] blkcg: s/RQ_QOS_CGROUP/RQ_QOS_LATENCY/ Tejun Heo 2019-08-28 22:05 ` [PATCH 07/10] blk-mq: add optional request->alloc_time_ns Tejun Heo 2019-08-28 22:05 ` [PATCH 08/10] blkcg: implement blk-iocost Tejun Heo 2019-08-29 15:53 ` [PATCH] blkcg: fix missing free on error path of blk_iocost_init() Tejun Heo 2019-09-10 12:55 ` [PATCH 08/10] blkcg: implement blk-iocost Michal Koutný 2019-09-10 16:08 ` Tejun Heo 2019-09-11 8:18 ` Paolo Valente 2019-09-11 14:16 ` Tejun Heo 2019-09-11 15:54 ` Tejun Heo 2019-09-11 16:44 ` Paolo Valente 2019-10-03 14:51 ` Michal Koutný 2019-10-03 16:45 ` Tejun Heo 2019-10-09 15:36 ` Michal Koutný 2019-10-14 15:36 ` Tejun Heo 2019-11-01 16:15 ` Michal Koutný 2019-11-01 16:56 ` Paolo Valente [this message] 2019-08-28 22:05 ` [PATCH 09/10] blkcg: add tools/cgroup/iocost_monitor.py Tejun Heo 2019-08-28 22:06 ` [PATCH 10/10] blkcg: add tools/cgroup/iocost_coef_gen.py Tejun Heo 2019-08-29 3:29 ` [PATCHSET v3 block/for-linus] IO cost model based work-conserving porportional controller Jens Axboe [not found] ` <20190829082248.6464-1-hdanton@sina.com> 2019-08-29 15:43 ` [PATCH 07/10] blk-mq: add optional request->alloc_time_ns Tejun Heo [not found] ` <20190829133928.16192-1-hdanton@sina.com> 2019-08-29 15:46 ` [PATCH 08/10] blkcg: implement blk-iocost Tejun Heo 2019-08-29 15:54 ` [PATCHSET v3 block/for-linus] IO cost model based work-conserving porportional controller Paolo Valente 2019-08-29 15:56 ` Tejun Heo -- strict thread matches above, loose matches on Subject: below -- 2019-07-10 20:51 [PATCHSET v2 " Tejun Heo 2019-07-10 20:51 ` [PATCH 08/10] blkcg: implement blk-iocost Tejun Heo
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