On Fri, Feb 9, 2018 at 11:53 AM, Juri Lelli <[email protected]> wrote: > Hi, > > On 09/02/18 11:36, Rafael J. Wysocki wrote: >> On Friday, February 9, 2018 9:02:34 AM CET Claudio Scordino wrote: >> > Hi Viresh, >> > >> > Il 09/02/2018 04:51, Viresh Kumar ha scritto: >> > > On 08-02-18, 18:01, Claudio Scordino wrote: >> > >> When the SCHED_DEADLINE scheduling class increases the CPU utilization, >> > >> we should not wait for the rate limit, otherwise we may miss some >> > >> deadline. >> > >> >> > >> Tests using rt-app on Exynos5422 have shown reductions of about 10% of >> > >> deadline >> > >> misses for tasks with low RT periods. >> > >> >> > >> The patch applies on top of the one recently proposed by Peter to drop >> > >> the >> > >> SCHED_CPUFREQ_* flags. >> > >> >> >> [cut] >> >> > >> > > >> > > Is it possible to (somehow) check here if the DL tasks will miss >> > > deadline if we continue to run at current frequency? And only ignore >> > > rate-limit if that is the case ? > > Isn't it always the case? Utilization associated to DL tasks is given by > what the user said it's needed to meet a task deadlines (admission > control). If that task wakes up and we realize that adding its > utilization contribution is going to require a frequency change, we > should _theoretically_ always do it, or it will be too late. Now, user > might have asked for a bit more than what strictly required (this is > usually the case to compensate for discrepancies between theory and real > world, e.g. hw transition limits), but I don't think there is a way to > know "how much". :/
You are right. I'm somewhat concerned about "fast switch" cases when the rate limit is used to reduce overhead.
