Messages in this thread | | | Date | Wed, 24 Jun 2020 17:55:00 +0100 | From | Qais Yousef <> | Subject | Re: [PATCH] cros_ec_spi: Even though we're RT priority, don't bump cpu freq |
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On 06/24/20 11:49, Joel Fernandes wrote: > On Tue, Jun 23, 2020 at 12:40 PM Qais Yousef <qais.yousef@arm.com> wrote: > > > > On 06/22/20 11:21, Doug Anderson wrote: > > > > [...] > > > > > > If you propose something that will help the discussion. I think based on the > > > > same approach Peter has taken to prevent random RT priorities. In uclamp case > > > > I think we just want to allow driver to opt RT tasks out of the default > > > > boosting behavior. > > > > > > > > I'm a bit wary that this extra layer of tuning might create a confusion, but > > > > I can't reason about why is it bad for a driver to say I don't want my RT task > > > > to be boosted too. > > > > > > Right. I was basically just trying to say "turn my boosting off". > > > > > > ...so I guess you're saying that doing a v2 of my patch with the > > > proper #ifdef protection wouldn't be a good way to go and I'd need to > > > propose some sort of API for this? > > > > It's up to Peter really. > > > > It concerns me in general to start having in-kernel users of uclamp that might > > end up setting random values (like we ended having random RT priorities), that > > really don't mean a lot outside the context of the specific system it was > > tested on. Given the kernel could run anywhere, it's hard to rationalize what's > > okay or not. > > > > Opting out of default RT boost for a specific task in the kernel, could make > > sense though it still concerns me for the same reasons. Is this okay for all > > possible systems this can run on? > > > > It feels better for userspace to turn RT boosting off for all tasks if you know > > your system is powerful, or use the per task API to switch off boosting for the > > tasks you know they don't need it. > > > > But if we want to allow in-kernel users, IMO it needs to be done in > > a controlled way, in a similar manner Peter changed how RT priority can be set > > in the kernel. > > > > It would be good hear what Peter thinks. > > It seems a bit of a hack, but really the commit message says the
Which part is the hack, the userspace control? It is how Linux expects things to work AFAIU. But I do agree there's a hole for general purpose userspace that wants to run and manage a diverse range of hardware.
I still think it's the job of device manufacturers/system integrator. But not many ship Linux by default. Though I thought ChromeOS is the exception here.
> driver is not expected to take a lot of CPU capacity so it should be > expected to work across platforms. It is likely to behave better than > how it behaves now.
Doing the in-kernel opt-out via API should be fine, I think. But this will need to be discussed in the wider circle. It will already clash with this for example
https://lore.kernel.org/lkml/20200619172011.5810-1-qais.yousef@arm.com/
Thanks
-- Qais Yousef
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