From: Bart Van Assche <Bart.VanAssche@sandisk.com>
To: "paolo.valente@linaro.org" <paolo.valente@linaro.org>,
"juri.lelli@arm.com" <juri.lelli@arm.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"patrick.bellasi@arm.com" <patrick.bellasi@arm.com>,
"axboe@kernel.dk" <axboe@kernel.dk>,
"joelaf@google.com" <joelaf@google.com>,
"andresoportus@google.com" <andresoportus@google.com>,
"morten.rasmussen@arm.com" <morten.rasmussen@arm.com>,
"aherrmann@suse.com" <aherrmann@suse.com>
Subject: Re: bfq-mq performance comparison to cfq
Date: Wed, 26 Apr 2017 22:12:36 +0000 [thread overview]
Message-ID: <1493244753.2632.22.camel@sandisk.com> (raw)
In-Reply-To: <AA9E8536-4CD0-4A67-80F4-90445C331C90@linaro.org>
On Wed, 2017-04-26 at 10:18 +0200, Paolo Valente wrote:
> I guess that both the above issues may not be dramatic. In contrast,
> the following last issue seems harder to address: BFQ uses two
> different privileging schemes, one suitable for interactive
> applications, and one suitable for soft real-time applications. So,
> what scheme should BFQ enable for processes in the RT I/O class?
>
> Because of these concerns, also for I/O I would find much clearer and
> flexible an ad-hoc, complete and explicit solution like the one(s)
> Juri reports (I've already nagged some of the recipients here to get
> support and collaboration on such sort of extensions of the basic
> benefits of a good I/O scheduler).
The numerical values of I/O priorities are part of the API between kernel
and user space API and hence the numerical value associated with a class
must not change. But we would associate different priority values with
interactive and soft real-time applications, e.g. IOPRIO_CLASS_RT(0) for
soft real-time applications and IOPRIO_CLASS_RT(7) for interactive
applications. See also http://man7.org/linux/man-pages/man2/ioprio_set.2.ht=
ml.
In my opinion the above proposal does not contradict with what has been
proposed for informed run-times. We could e.g. add support for configuring
the I/O priority to the block I/O controller cgroup.
No matter how informed run-times communicate application constraints to the
kernel, the configured I/O scheduler and the block layer will have to reali=
ze
these constraints. If anyone thinks that there is a mechanism that is bette=
r
suited to communicate these constraints to the kernel than I/O priorities I=
'm
interested to hear about that alternative.
Bart.=
WARNING: multiple messages have this Message-ID (diff)
From: Bart Van Assche <Bart.VanAssche@sandisk.com>
To: "paolo.valente@linaro.org" <paolo.valente@linaro.org>,
"juri.lelli@arm.com" <juri.lelli@arm.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"patrick.bellasi@arm.com" <patrick.bellasi@arm.com>,
"axboe@kernel.dk" <axboe@kernel.dk>,
"joelaf@google.com" <joelaf@google.com>,
"andresoportus@google.com" <andresoportus@google.com>,
"morten.rasmussen@arm.com" <morten.rasmussen@arm.com>,
"aherrmann@suse.com" <aherrmann@suse.com>
Subject: Re: bfq-mq performance comparison to cfq
Date: Wed, 26 Apr 2017 22:12:36 +0000 [thread overview]
Message-ID: <1493244753.2632.22.camel@sandisk.com> (raw)
In-Reply-To: <AA9E8536-4CD0-4A67-80F4-90445C331C90@linaro.org>
On Wed, 2017-04-26 at 10:18 +0200, Paolo Valente wrote:
> I guess that both the above issues may not be dramatic. In contrast,
> the following last issue seems harder to address: BFQ uses two
> different privileging schemes, one suitable for interactive
> applications, and one suitable for soft real-time applications. So,
> what scheme should BFQ enable for processes in the RT I/O class?
>
> Because of these concerns, also for I/O I would find much clearer and
> flexible an ad-hoc, complete and explicit solution like the one(s)
> Juri reports (I've already nagged some of the recipients here to get
> support and collaboration on such sort of extensions of the basic
> benefits of a good I/O scheduler).
The numerical values of I/O priorities are part of the API between kernel
and user space API and hence the numerical value associated with a class
must not change. But we would associate different priority values with
interactive and soft real-time applications, e.g. IOPRIO_CLASS_RT(0) for
soft real-time applications and IOPRIO_CLASS_RT(7) for interactive
applications. See also http://man7.org/linux/man-pages/man2/ioprio_set.2.html.
In my opinion the above proposal does not contradict with what has been
proposed for informed run-times. We could e.g. add support for configuring
the I/O priority to the block I/O controller cgroup.
No matter how informed run-times communicate application constraints to the
kernel, the configured I/O scheduler and the block layer will have to realize
these constraints. If anyone thinks that there is a mechanism that is better
suited to communicate these constraints to the kernel than I/O priorities I'm
interested to hear about that alternative.
Bart.
next prev parent reply other threads:[~2017-04-26 22:12 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
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 [this message]
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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