Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 27 Jan 2023 23:29:16 +0100 | Subject | Re: [bug-report] possible s64 overflow in max_vruntime() |
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On Fri, 27 Jan 2023 at 23:10, Benjamin Segall <bsegall@google.com> wrote: > > Vincent Guittot <vincent.guittot@linaro.org> writes: > > > On Fri, 27 Jan 2023 at 12:44, Peter Zijlstra <peterz@infradead.org> wrote: > >> > >> On Thu, Jan 26, 2023 at 07:31:02PM +0100, Roman Kagan wrote: > >> > >> > > All that only matters for small sleeps anyway. > >> > > > >> > > Something like: > >> > > > >> > > sleep_time = U64_MAX; > >> > > if (se->avg.last_update_time) > >> > > sleep_time = cfs_rq_clock_pelt(cfs_rq) - se->avg.last_update_time; > >> > > >> > Interesting, why not rq_clock_task(rq_of(cfs_rq)) - se->exec_start, as > >> > others were suggesting? It appears to better match the notion of sleep > >> > wall-time, no? > >> > >> Should also work I suppose. cfs_rq_clock takes throttling into account, > >> but that should hopefully also not be *that* long, so either should > >> work. > > > > yes rq_clock_task(rq_of(cfs_rq)) should be fine too > > No, last_update_time is based on cfs_rq_clock_pelt(cfs_rq), and it will > get more and more out of sync as time goes on, every time the cfs_rq > throttles. It won't reset when the throttle is done.
I was referring to the rq_clock_task(rq_of(cfs_rq)) - se->exec_start that Roman was asking for
> > > > > Another thing to take into account is the sleeper credit that the > > waking task deserves so the detection should be done once it has been > > subtracted from vruntime. > > > > Last point, when a nice -20 task runs on a rq, it will take a bit more > > than 2 seconds for the vruntime to be increased by more than 24ms (the > > maximum credit that a waking task can get) so threshold must be > > significantly higher than 2 sec. On the opposite side, the lowest > > possible weight of a cfs rq is 2 which means that the problem appears > > for a sleep longer or equal to 2^54 = 2^63*2/1024. We should use this > > value instead of an arbitrary 200 days
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