On 2020/8/14 12:04, benbjiang(蒋彪) wrote:
>
>
>> On Aug 14, 2020, at 9:36 AM, Li, Aubrey <aubrey...@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...@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
