Messages in this thread | | | Subject | Re: [RFC PATCH v2 07/13] firmware: arm_scmi: Add notification dispatch and delivery | From | Lukasz Luba <> | Date | Mon, 24 Feb 2020 09:59:55 +0000 |
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On 2/21/20 7:11 PM, Lukasz Luba wrote: > > > On 2/21/20 7:01 PM, Cristian Marussi wrote: >> Hi Lukasz >> >> Thanks for your feedback ! >> >> On 21/02/2020 13:25, Lukasz Luba wrote: >>> Hi Cristian, >>> >>> I didn't want to jump into your discussion with Jim in other broader >>> thread with this small thought, so I added a comment below. >>> >>> On 2/14/20 3:35 PM, Cristian Marussi wrote: >>>> Add core SCMI Notifications dispatch and delivery support logic >>>> which is >>> [snip] >>> >>>> @@ -840,6 +1071,11 @@ static struct scmi_notify_ops notify_ops = { >>>> */ >>>> int scmi_notification_init(struct scmi_handle *handle) >>>> { >>>> + scmi_notify_wq = alloc_workqueue("scmi_notify", >>>> + WQ_UNBOUND | WQ_FREEZABLE, 0); >>> >>> I think it might limit some platforms. It depends on their workload. >>> If they have some high priority workloads which rely on this mechanisms, >>> they might need a RT task here. The workqueues would be scheduled in >>> CFS, so it depends on workload in there (we might even see 10s ms delays >>> in scheduling-up them). If we use RT we would grab the CPU from CFS. >>> >>> It would be good if it is a customization option: which mechanism >>> to use based on some a parameter. Then we could create: >>> a) workqueue with the flags above >>> b) workqueue with WQ_HIGHPRI (limited by minimum nice) >>> c) kthread_create_worker() with RT/DL/FIFO sched policy >>> (with also a parameterized priority) >>> In default clients might use a) but when they want to tune their >>> platform, they might change only a parameter in their scmi code, >>> not maintaining a patch for the RT function out of tree. >> >> In this series, I have not addressed configurability issues at all (as >> noted in the cover): >> in fact I was thinking that stuff like WQ_HIGHPRI flags and >> per-protocol queue sizes could >> be beneficial to be customizable depending on the specific platform, >> but I had not gone to >> the extreme of thinking of adopting a dedicated RT kthread as a >> worker...good point...it >> makes surely sense to have this configurable option to try to reduce >> the latency where possible. >> >> I think it's important to give the user the possibility to configure >> the deferred worker >> as you suggested, if the user decides to rely on Linux to handle a >> critical notification, >> but I'd prefer queuing up this work you suggested on a different >> series on top of this one. >> (which is starting to be a little to much voluminous...for being just >> the core support) > > Agree, you can build these features incrementally.
Although, a WQ_SYSFS flag wouldn't harm too much this version and might give possibility to tune/experiment with it.
> > Regards, > Lukasz >
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