From: Paolo Valente <paolo.valente@linaro.org> To: Bart Van Assche <bart.vanassche@sandisk.com> Cc: "aherrmann@suse.com" <aherrmann@suse.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>, "axboe@kernel.dk" <axboe@kernel.dk> Subject: Re: bfq-mq performance comparison to cfq Date: Wed, 19 Apr 2017 09:02:49 +0200 [thread overview] Message-ID: <4C1ABADD-6751-45E4-8DA1-ACA5A9E1379D@linaro.org> (raw) In-Reply-To: <CY1PR0401MB15362FAB3D841CDF2C421A2981180@CY1PR0401MB1536.namprd04.prod.outlook.com> > Il giorno 19 apr 2017, alle ore 07:01, Bart Van Assche = <bart.vanassche@sandisk.com> ha scritto: >=20 > On 04/11/17 00:29, Paolo Valente wrote: >>=20 >>> Il giorno 10 apr 2017, alle ore 17:15, Bart Van Assche = <bart.vanassche@sandisk.com> ha scritto: >>>=20 >>> On Mon, 2017-04-10 at 11:55 +0200, Paolo Valente wrote: >>>> That said, if you do always want maximum throughput, even at the >>>> expense of latency, then just switch off low-latency heuristics, = i.e., >>>> set low_latency to 0. Depending on the device, setting slice_ilde = to >>>> 0 may help a lot too (as well as with CFQ). If the throughput is >>>> still low also after forcing BFQ to an only-throughput mode, then = you >>>> hit some bug, and I'll have a little more work to do ... >>>=20 >>> Has it been considered to make applications tell the I/O scheduler >>> whether to optimize for latency or for throughput? It shouldn't be = that >>> hard for window managers and shells to figure out whether or not a = new >>> application that is being started is interactive or not. This would >>> require a mechanism that allows applications to provide such = information >>> to the I/O scheduler. Wouldn't that be a better approach than the = I/O >>> scheduler trying to guess whether or not an application is an = interactive >>> application? >>=20 >> IMO that would be an (or maybe the) optimal solution, in terms of = both >> throughput and latency. We have even developed a prototype doing = what >> you propose, for Android. Unfortunately, I have not yet succeeded in >> getting support, to turn it into candidate production code, or to = make >> a similar solution for lsb-compliant systems. >=20 > Hello Paolo, >=20 > What API was used by the Android application to tell the I/O scheduler=20= > to optimize for latency? Do you think that it would be sufficient if = the=20 > application uses the ioprio_set() system call to set the I/O priority = to=20 > IOPRIO_CLASS_RT? >=20 That's exactly the hack we are using in our prototype. However, it can only be a temporary hack, because it mixes two slightly different concepts: 1) the activation of weight raising and other mechanisms for reducing latency for the target app, 2) the assignment of a different priority class, which (cleanly) means just that processes in a lower priority class will be served only when the processes of the target app have no pending I/O request. Finding a clean boosting API would be one of the main steps to turn our prototype into a usable solution. Thanks, Paolo > Thanks, >=20 > Bart.
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Valente <paolo.valente@linaro.org> To: Bart Van Assche <bart.vanassche@sandisk.com> Cc: "aherrmann@suse.com" <aherrmann@suse.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>, "axboe@kernel.dk" <axboe@kernel.dk> Subject: Re: bfq-mq performance comparison to cfq Date: Wed, 19 Apr 2017 09:02:49 +0200 [thread overview] Message-ID: <4C1ABADD-6751-45E4-8DA1-ACA5A9E1379D@linaro.org> (raw) In-Reply-To: <CY1PR0401MB15362FAB3D841CDF2C421A2981180@CY1PR0401MB1536.namprd04.prod.outlook.com> > Il giorno 19 apr 2017, alle ore 07:01, Bart Van Assche <bart.vanassche@sandisk.com> ha scritto: > > On 04/11/17 00:29, Paolo Valente wrote: >> >>> Il giorno 10 apr 2017, alle ore 17:15, Bart Van Assche <bart.vanassche@sandisk.com> ha scritto: >>> >>> On Mon, 2017-04-10 at 11:55 +0200, Paolo Valente wrote: >>>> That said, if you do always want maximum throughput, even at the >>>> expense of latency, then just switch off low-latency heuristics, i.e., >>>> set low_latency to 0. Depending on the device, setting slice_ilde to >>>> 0 may help a lot too (as well as with CFQ). If the throughput is >>>> still low also after forcing BFQ to an only-throughput mode, then you >>>> hit some bug, and I'll have a little more work to do ... >>> >>> Has it been considered to make applications tell the I/O scheduler >>> whether to optimize for latency or for throughput? It shouldn't be that >>> hard for window managers and shells to figure out whether or not a new >>> application that is being started is interactive or not. This would >>> require a mechanism that allows applications to provide such information >>> to the I/O scheduler. Wouldn't that be a better approach than the I/O >>> scheduler trying to guess whether or not an application is an interactive >>> application? >> >> IMO that would be an (or maybe the) optimal solution, in terms of both >> throughput and latency. We have even developed a prototype doing what >> you propose, for Android. Unfortunately, I have not yet succeeded in >> getting support, to turn it into candidate production code, or to make >> a similar solution for lsb-compliant systems. > > Hello Paolo, > > What API was used by the Android application to tell the I/O scheduler > to optimize for latency? Do you think that it would be sufficient if the > application uses the ioprio_set() system call to set the I/O priority to > IOPRIO_CLASS_RT? > That's exactly the hack we are using in our prototype. However, it can only be a temporary hack, because it mixes two slightly different concepts: 1) the activation of weight raising and other mechanisms for reducing latency for the target app, 2) the assignment of a different priority class, which (cleanly) means just that processes in a lower priority class will be served only when the processes of the target app have no pending I/O request. Finding a clean boosting API would be one of the main steps to turn our prototype into a usable solution. Thanks, Paolo > Thanks, > > Bart.
next prev parent reply other threads:[~2017-04-19 7:02 UTC|newest] Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-04-10 9:05 bfq-mq performance comparison to cfq Andreas Herrmann 2017-04-10 9:55 ` Paolo Valente 2017-04-10 9:55 ` Paolo Valente 2017-04-10 15:15 ` Bart Van Assche 2017-04-10 15:15 ` Bart Van Assche 2017-04-11 7:29 ` Paolo Valente 2017-04-11 7:29 ` Paolo Valente 2017-04-19 5:01 ` Bart Van Assche 2017-04-19 5:01 ` Bart Van Assche 2017-04-19 7:02 ` Paolo Valente [this message] 2017-04-19 7:02 ` Paolo Valente 2017-04-19 15:43 ` Bart Van Assche 2017-04-19 15:43 ` Bart Van Assche 2017-04-25 9:40 ` Juri Lelli 2017-04-26 8:18 ` Paolo Valente 2017-04-26 8:18 ` Paolo Valente 2017-04-26 22:12 ` Bart Van Assche 2017-04-26 22:12 ` Bart Van Assche 2017-04-11 7:26 ` Paolo Valente 2017-04-11 7:26 ` Paolo Valente 2017-04-11 16:31 ` Andreas Herrmann
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