Messages in this thread | | | From | Vincent Guittot <> | Date | Tue, 28 Mar 2017 11:29:31 +0200 | Subject | Re: [RFD PATCH 3/5] sched/cpufreq_schedutil: make worker kthread be SCHED_DEADLINE |
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On 27 March 2017 at 18:50, Peter Zijlstra <peterz@infradead.org> wrote: > 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.
But sending new voltage value to PMIC is only part of the sequence. When cpufreq set a new opp, it does
-set new voltage -wait for the voltage to settle down. -set the new clock frequency
you can even have to switch to an intermediate clock source.
When such sequence is managed by the kernel, we can't easily git ride of a kthread
> > > 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?
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