From: Marc Zyngier <maz@kernel.org>
To: Qais Yousef <qais.yousef@arm.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Yury Norov <yury.norov@gmail.com>, Paul Turner <pjt@google.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Josh Don <joshdon@google.com>,
Pavan Kondeti <pkondeti@codeaurora.org>,
linux-kernel@vger.kernel.org,
"Rafael J. Wysocki" <rjw@rjwysocki.net>
Subject: Re: [PATCH 0/4] sched/rt: Distribute tasks in find_lowest_rq()
Date: Tue, 21 Apr 2020 15:28:23 +0100 [thread overview]
Message-ID: <1c21b8e7b08e6db7fb97dc46d1246d9a@kernel.org> (raw)
In-Reply-To: <20200421142243.lea26mnmxnjpynlf@e107158-lin.cambridge.arm.com>
On 2020-04-21 15:22, Qais Yousef wrote:
> On 04/21/20 15:09, Marc Zyngier wrote:
>> On 2020-04-21 14:18, Valentin Schneider wrote:
>> > On 21/04/20 13:13, Qais Yousef wrote:
>>
>> [...]
>>
>> > > I CCed Marc who's the maintainer of this file who can clarify better
>> > > if this
>> > > really breaks anything.
>> > >
>> > > If any interrupt expects to be affined to a specific CPU then this
>> > > must be
>> > > described in DT/driver. I think the GIC controller is free to
>> > > distribute them
>> > > to any cpu otherwise if !force. Which is usually done by
>> > > irq_balancer anyway
>> > > in userspace, IIUC.
>> > >
>> > > I don't see how cpumask_any_and() break anything here too. I
>> > > actually think it
>> > > improves on things by better distribute the irqs on the system by
>> > > default.
>>
>> That's a pretty bold statement. Unfortunately, it isn't universally
>> true.
>> Some workload will be very happy with interrupts spread all over the
>> map,
>> and some others will suffer from it because, well, it interrupts
>> userspace.
>>
>> > As you say, if someone wants smarter IRQ affinity they can do
>> > irq_balancer
>> > and whatnot. The default kernel policy for now has been to shove
>> > everything
>> > on the lowest-numbered CPU, and I see no valid reason to change that.
>>
>> Exactly. I would like to keep the kernel policy as simple as possible
>> for
>> non-managed interrupts (managed interrupts are another kettle of fish
>> entirely).
>> Userpace is in control to place things "intelligently", so let's not
>> try and
>> make the kernel smarter than it strictly needs to be.
>
> Fair enough. But why is it asking for cpumask_any() in the first place?
Implementation detail. Turn it into cpumask_first_and() if you want.
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2020-04-21 14:28 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 15:05 [PATCH 0/4] sched/rt: Distribute tasks in find_lowest_rq() Qais Yousef
2020-04-14 15:05 ` [PATCH 1/4] cpumask: Rename cpumask_any_and_distribute Qais Yousef
2020-04-14 15:05 ` [PATCH 2/4] cpumask: Make cpumask_any() truly random Qais Yousef
2020-04-14 16:19 ` Steven Rostedt
2020-04-15 9:36 ` Peter Zijlstra
2020-04-20 15:43 ` Qais Yousef
2020-04-20 21:36 ` Josh Don
2020-05-28 8:52 ` [cpumask] a7934287d8: BUG:using__this_cpu_read()in_preemptible[#]code:kworker kernel test robot
2020-05-28 8:52 ` kernel test robot
2020-04-14 15:05 ` [PATCH 3/4] cpumask: Convert cpumask_any_but() to the new random function Qais Yousef
2020-04-14 16:28 ` Steven Rostedt
2020-04-20 15:49 ` Qais Yousef
2020-04-14 15:05 ` [PATCH 4/4] sched/rt: Better distribute tasks that wakeup simultaneously Qais Yousef
2020-04-14 18:58 ` [PATCH 0/4] sched/rt: Distribute tasks in find_lowest_rq() Valentin Schneider
2020-04-14 20:27 ` Steven Rostedt
2020-04-14 20:56 ` Valentin Schneider
2020-04-15 9:39 ` Peter Zijlstra
2020-04-15 13:18 ` Steven Rostedt
2020-04-21 12:15 ` Qais Yousef
2020-04-21 12:13 ` Qais Yousef
2020-04-21 13:18 ` Valentin Schneider
2020-04-21 13:28 ` Vincent Guittot
2020-04-21 14:22 ` Yury Norov
2020-04-21 14:25 ` Qais Yousef
2020-04-21 14:09 ` Marc Zyngier
2020-04-21 14:22 ` Qais Yousef
2020-04-21 14:28 ` Marc Zyngier [this message]
2020-04-21 14:39 ` Qais Yousef
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