On 2020/8/14 8:26, benbjiang(蒋彪) wrote: > > >> On Aug 13, 2020, at 12:28 PM, Li, Aubrey <aubrey...@linux.intel.com> wrote: >> >> On 2020/8/13 7:08, Joel Fernandes wrote: >>> On Wed, Aug 12, 2020 at 10:01:24AM +0800, Li, Aubrey wrote: >>>> Hi Joel, >>>> >>>> On 2020/8/10 0:44, Joel Fernandes wrote: >>>>> Hi Aubrey, >>>>> >>>>> Apologies for replying late as I was still looking into the details. >>>>> >>>>> On Wed, Aug 05, 2020 at 11:57:20AM +0800, Li, Aubrey wrote: >>>>> [...] >>>>>> +/* >>>>>> + * Core scheduling policy: >>>>>> + * - CORE_SCHED_DISABLED: core scheduling is disabled. >>>>>> + * - CORE_COOKIE_MATCH: tasks with same cookie can run >>>>>> + * on the same core concurrently. >>>>>> + * - CORE_COOKIE_TRUST: trusted task can run with kernel >>>>>> thread on the same core concurrently. >>>>>> + * - CORE_COOKIE_LONELY: tasks with cookie can run only >>>>>> + * with idle thread on the same core. >>>>>> + */ >>>>>> +enum coresched_policy { >>>>>> + CORE_SCHED_DISABLED, >>>>>> + CORE_SCHED_COOKIE_MATCH, >>>>>> + CORE_SCHED_COOKIE_TRUST, >>>>>> + CORE_SCHED_COOKIE_LONELY, >>>>>> +}; >>>>>> >>>>>> We can set policy to CORE_COOKIE_TRUST of uperf cgroup and fix this kind >>>>>> of performance regression. Not sure if this sounds attractive? >>>>> >>>>> Instead of this, I think it can be something simpler IMHO: >>>>> >>>>> 1. Consider all cookie-0 task as trusted. (Even right now, if you apply >>>>> the >>>>> core-scheduling patchset, such tasks will share a core and sniff on each >>>>> other. So let us not pretend that such tasks are not trusted). >>>>> >>>>> 2. All kernel threads and idle task would have a cookie 0 (so that will >>>>> cover >>>>> ksoftirqd reported in your original issue). >>>>> >>>>> 3. Add a config option (CONFIG_SCHED_CORE_DEFAULT_TASKS_UNTRUSTED). >>>>> Default >>>>> enable it. Setting this option would tag all tasks that are forked from >>>>> a >>>>> cookie-0 task with their own cookie. Later on, such tasks can be added >>>>> to >>>>> a group. This cover's PeterZ's ask about having 'default untrusted'). >>>>> (Users like ChromeOS that don't want to userspace system processes to be >>>>> tagged can disable this option so such tasks will be cookie-0). >>>>> >>>>> 4. Allow prctl/cgroup interfaces to create groups of tasks and override >>>>> the >>>>> above behaviors. >>>> >>>> How does uperf in a cgroup work with ksoftirqd? Are you suggesting I set >>>> uperf's >>>> cookie to be cookie-0 via prctl? >>> >>> Yes, but let me try to understand better. There are 2 problems here I think: >>> >>> 1. ksoftirqd getting idled when HT is turned on, because uperf is sharing a >>> core with it: This should not be any worse than SMT OFF, because even SMT >>> OFF >>> would also reduce ksoftirqd's CPU time just core sched is doing. Sure >>> core-scheduling adds some overhead with IPIs but such a huge drop of perf is >>> strange. Peter any thoughts on that? >>> >>> 2. Interface: To solve the performance problem, you are saying you want >>> uperf >>> to share a core with ksoftirqd so that it is not forced into idle. Why not >>> just keep uperf out of the cgroup? >> >> I guess this is unacceptable for who runs their apps in container and vm. > IMHO, just as Joel proposed, > 1. Consider all cookie-0 task as trusted. > 2. All kernel threads and idle task would have a cookie 0 > In that way, all tasks with cookies(including uperf in a cgroup) could run > concurrently with kernel threads. > That could be a good solution for the issue. :)
>From uperf point of review, it can trust cookie-0(I assume we still need some modifications to change cookie-match to cookie-compatible to allow ZERO and NONZERO run together). But from kernel thread point of review, it can NOT trust uperf, unless we set uperf's cookie to 0. Thanks, -Aubrey