lkml.org 
[lkml]   [2017]   [Dec]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/4] sched: cpufreq: Keep track of cpufreq utilization update flags
On Wed, Dec 13, 2017 at 03:23:21PM +0530, Viresh Kumar wrote:
> Currently the schedutil governor overwrites the sg_cpu->flags field on
> every call to the utilization handler. It was pretty good as the initial
> implementation of utilization handlers, there are several drawbacks
> though.
>
> The biggest drawback is that the sg_cpu->flags field doesn't always
> represent the correct type of tasks that are enqueued on a CPU's rq. For
> example, if a fair task is enqueued while a RT or DL task is running, we
> will overwrite the flags with value 0 and that may take the CPU to lower
> OPPs unintentionally. There can be other corner cases as well which we
> aren't aware of currently.
>
> This patch changes the current implementation to keep track of all the
> task types that are currently enqueued to the CPUs rq. A new flag: CLEAR
> is introduced and is set by the scheduling classes when their last task
> is dequeued. When the CLEAR flag bit is set, the schedutil governor resets
> all the other flag bits that are present in the flags parameter. For
> now, the util update handlers return immediately if they were called to
> clear the flag.

Yeah, not happy about this either; we had code that did the right thing
without this extra tracking I think.

Also, we can look at the rq state if we want to, we don't need to
duplicate that state.

\
 
 \ /
  Last update: 2017-12-19 20:25    [W:1.415 / U:0.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site