Messages in this thread | | | Subject | Re: [RFC PATCH 00/16] Core scheduling v6(Internet mail) | From | "Li, Aubrey" <> | Date | Fri, 14 Aug 2020 13:18:02 +0800 |
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On 2020/8/14 12:04, benbjiang(蒋彪) wrote: > > >> On Aug 14, 2020, at 9:36 AM, Li, Aubrey <aubrey.li@linux.intel.com> wrote: >> >> On 2020/8/14 8:26, benbjiang(蒋彪) wrote: >>> >>> >>>> On Aug 13, 2020, at 12:28 PM, Li, Aubrey <aubrey.li@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. > That’s right. :) > Could we set the cookie of cgroup where uperf lies to 0? > IMHO the disadvantage is that if there are two or more cgroups set cookie-0, then the user applications in these cgroups could run concurrently on a core, though all of them are set as trusted, we made a hole of user->user isolation.
Thanks, -Aubrey
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