On 20-Dec 15:52, Rafael J. Wysocki wrote: > On Wednesday, December 20, 2017 3:31:00 PM CET Patrick Bellasi wrote: > > On 20-Dec 14:28, Peter Zijlstra wrote: > > > On Wed, Dec 20, 2017 at 12:55:46PM +0000, Patrick Bellasi wrote: > > > > On 20-Dec 09:31, Peter Zijlstra wrote: > > > > > > > > Didn't juri have patches to make DL do something sane? But yes, I > > > > > think > > > > > those flags are part of the problem. > > > > > > > > He recently reposted them here: > > > > > > > > https://lkml.kernel.org/r/20171204102325.5110-1-juri.le...@redhat.com > > > > > > Yeah, just found them and actually munged them into my queue; did all > > > the modifications you suggested too. Lets see if it comes apart. > > > > > > > > > - From the utilization handler, we check runqueues of all three > > > > > > sched > > > > > > classes to see if they have some work pending (this can be done > > > > > > smartly by checking only RT first and skipping other checks if RT > > > > > > has some work). > > > > > > > > > > No that's wrong. DL should provide a minimum required based on > > > > > existing > > > > > reservations, we can add the expected CFS average on top and request > > > > > that. > > > > > > > > > > And for RT all we need to know is if current is of that class, > > > > > otherwise > > > > > we don't care. > > > > > > > > So, this: > > > > > > > > https://marc.info/?i=20171130114723.29210-3-patrick.bellasi%40arm.com > > > > > > Right, I was actually looking for those patches, but I'm searching > > > backwards and hit upon Juri's patches first. > > > > > > > was actually going in this direction, although still working on top of > > > > flags to not change the existing interface too much. > > > > > > > > IMO, the advantage of flags is that they are a sort-of "pro-active" > > > > approach, where the scheduler notify sensible events to schedutil. > > > > But keep adding flags seems to overkilling to me too. > > > > > > > > If we remove flags then we have to query the scheduler classes "on > > > > demand"... but, as Peter suggests, once we have DL bits Juri posted, > > > > the only issue if to know if an RT task is running. > > > > This the patch above can be just good enough, with no flags at all and > > > > with just a check for current being RT (or DL for the time being). > > > > > > Well, we still need flags for crap like IO-WAIT IIRC. That's sugov > > > internal state and not something the scheduler actually already knows. > > > > Right, that flag is set from: > > > > core.c::io_schedule_prepare() > > > > for the current task, which is going to be dequeued soon. > > > > Once it wakes up the next time, at enqueue time we trigger a boosting > > by passing schedutil that flag. > > > > Thus, unless we are happy to delay the boosting until the task is > > actually picked for execution (don't think so), then we need to keep > > the flag and signal schedutil at enqueue time. > > > > However, was wondering one thing: should't we already have a vruntime > > bonus for IO sleeping tasks? Because in that case, the task is likely > > to be on CPU quite soon... and thus, perhaps by removing the flag and > > moving the schedutil notification into core.c at the end of > > __schedule() should be working to detect both RT and FAIR::IOWAIT > > boosted tasks. > > schedutil is not the only user of this flag.
Sure, but with the idea above (not completely sure it makes sense) intel_pstate_update_util() can still get the IIOWAIT information. We just get that info from current->in_iowait instead of checking a flag which is passed in via callback. > Thanks, > Rafael > -- #include <best/regards.h> Patrick Bellasi
