From: Peter Zijlstra <peterz@infradead.org>
To: Juri Lelli <juri.lelli@arm.com>
Cc: mingo@redhat.com, rjw@rjwysocki.net, viresh.kumar@linaro.org,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
tglx@linutronix.de, vincent.guittot@linaro.org,
rostedt@goodmis.org, luca.abeni@santannapisa.it,
claudio@evidence.eu.com, tommaso.cucinotta@santannapisa.it,
bristot@redhat.com, mathieu.poirier@linaro.org,
tkjos@android.com, joelaf@google.com, andresoportus@google.com,
morten.rasmussen@arm.com, dietmar.eggemann@arm.com,
patrick.bellasi@arm.com, Ingo Molnar <mingo@kernel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Mark Brown <broonie@kernel.org>
Subject: Re: [RFD PATCH 3/5] sched/cpufreq_schedutil: make worker kthread be SCHED_DEADLINE
Date: Mon, 27 Mar 2017 18:50:11 +0200 [thread overview]
Message-ID: <20170327165011.dpip23cyolnleas6@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20170324140900.7334-4-juri.lelli@arm.com>
On Fri, Mar 24, 2017 at 02:08:58PM +0000, Juri Lelli wrote:
> Worker kthread needs to be able to change frequency for all other
> threads.
>
> Make it special, just under STOP class.
*yuck* ;-)
So imagine our I2C/SPI bus is 'busy' and its mutex taken, then this
'soecial' task will need to boost it. Now add BWI to your thinking and
shudder.
On IRC broonie mentioned that:
- most PMIC operations are fire and forget (no need to wait for a
response).
- PMIC 'packets' are 'small'.
- SPI has the possibility to push stuff on the queue.
Taken together this seems to suggest we can rework cpufreq drivers to
function in-context, either directly push the packet on the bus if
available, or queue it and let whoever owns it sort it without blocking.
It might be possible to rework/augment I2C to also support pushing stuff
on a queue.
So if we can make all that work, we can do away with this horrible
horrible kthread. Which is, IMO, a much better solution.
Thoughts?
next prev parent reply other threads:[~2017-03-27 16:50 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-24 14:08 [RFD PATCH 0/5] SCHED_DEADLINE freq/cpu invariance and OPP selection Juri Lelli
2017-03-24 14:08 ` [RFD PATCH 1/5] sched/cpufreq_schedutil: make use of DEADLINE utilization signal Juri Lelli
2017-03-24 14:08 ` [RFD PATCH 2/5] sched/deadline: move cpu frequency selection triggering points Juri Lelli
2017-03-24 14:08 ` [RFD PATCH 3/5] sched/cpufreq_schedutil: make worker kthread be SCHED_DEADLINE Juri Lelli
2017-03-27 16:50 ` Peter Zijlstra [this message]
2017-03-27 17:01 ` Juri Lelli
2017-03-27 17:05 ` Rafael J. Wysocki
2017-03-27 17:13 ` Juri Lelli
2017-03-27 17:37 ` Rafael J. Wysocki
2017-03-27 18:09 ` Mark Brown
2017-03-30 15:50 ` Vikram Mulukutla
2017-03-30 20:22 ` Rafael J. Wysocki
2017-03-31 7:26 ` Juri Lelli
2017-03-27 18:05 ` Mark Brown
2017-03-28 9:29 ` Vincent Guittot
2017-03-28 10:20 ` Peter Zijlstra
2017-03-24 14:08 ` [RFD PATCH 4/5] sched/cpufreq_schedutil: always consider all CPUs when deciding next freq Juri Lelli
2017-03-29 22:41 ` Rafael J. Wysocki
2017-03-30 8:58 ` Juri Lelli
2017-03-30 13:21 ` Vincent Guittot
2017-03-30 20:13 ` Rafael J. Wysocki
2017-03-31 7:31 ` Juri Lelli
2017-03-31 9:03 ` Rafael J. Wysocki
2017-03-31 9:16 ` Juri Lelli
2017-03-24 14:09 ` [RFD PATCH 5/5] sched/deadline: make bandwidth enforcement scale-invariant Juri Lelli
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