Messages in this thread | | | Subject | Re: [RFC PATCH v2 11/17] sched: Basic tracking of matching tasks | From | Subhra Mazumdar <> | Date | Wed, 8 May 2019 19:14:17 -0700 |
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On 5/8/19 6:38 PM, Aubrey Li wrote: > On Thu, May 9, 2019 at 8:29 AM Subhra Mazumdar > <subhra.mazumdar@oracle.com> wrote: >> >> On 5/8/19 5:01 PM, Aubrey Li wrote: >>> On Thu, May 9, 2019 at 2:41 AM Subhra Mazumdar >>> <subhra.mazumdar@oracle.com> wrote: >>>> On 5/8/19 11:19 AM, Subhra Mazumdar wrote: >>>>> On 5/8/19 8:49 AM, Aubrey Li wrote: >>>>>>> Pawan ran an experiment setting up 2 VMs, with one VM doing a >>>>>>> parallel kernel build and one VM doing sysbench, >>>>>>> limiting both VMs to run on 16 cpu threads (8 physical cores), with >>>>>>> 8 vcpu for each VM. >>>>>>> Making the fix did improve kernel build time by 7%. >>>>>> I'm gonna agree with the patch below, but just wonder if the testing >>>>>> result is consistent, >>>>>> as I didn't see any improvement in my testing environment. >>>>>> >>>>>> IIUC, from the code behavior, especially for 2 VMs case(only 2 >>>>>> different cookies), the >>>>>> per-rq rb tree unlikely has nodes with different cookies, that is, all >>>>>> the nodes on this >>>>>> tree should have the same cookie, so: >>>>>> - if the parameter cookie is equal to the rb tree cookie, we meet a >>>>>> match and go the >>>>>> third branch >>>>>> - else, no matter we go left or right, we can't find a match, and >>>>>> we'll return idle thread >>>>>> finally. >>>>>> >>>>>> Please correct me if I was wrong. >>>>>> >>>>>> Thanks, >>>>>> -Aubrey >>>>> This is searching in the per core rb tree (rq->core_tree) which can have >>>>> 2 different cookies. But having said that, even I didn't see any >>>>> improvement with the patch for my DB test case. But logically it is >>>>> correct. >>>>> >>>> Ah, my bad. It is per rq. But still can have 2 different cookies. Not sure >>>> why you think it is unlikely? >>> Yeah, I meant 2 different cookies on the system, but unlikely 2 >>> different cookies >>> on one same rq. >>> >>> If I read the source correctly, for the sched_core_balance path, when try to >>> steal cookie from another CPU, sched_core_find() uses dst's cookie to search >>> if there is a cookie match in src's rq, and sched_core_find() returns idle or >>> matched task, and later put this matched task onto dst's rq (activate_task() in >>> sched_core_find()). At this moment, the nodes on the rq's rb tree should have >>> same cookies. >>> >>> Thanks, >>> -Aubrey >> Yes, but sched_core_find is also called from pick_task to find a local >> matching task. > Can a local searching introduce a different cookies? Where is it from? No. I meant the local search uses the same binary search of sched_core_find so it has to be correct. > >> The enqueue side logic of the scheduler is unchanged with >> core scheduling, > But only the task with cookies is placed onto this rb tree? > >> so it is possible tasks with different cookies are >> enqueued on the same rq. So while searching for a matching task locally >> doing it correctly should matter. > May I know how exactly? select_task_rq_* seems to be unchanged. So the search logic to find a cpu to enqueue when a task becomes runnable is same as before and doesn't do any kind of cookie matching. > > Thanks, > -Aubrey
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