On Thu, May 9, 2019 at 8:29 AM Subhra Mazumdar <subhra.mazum...@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.mazum...@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? > 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? Thanks, -Aubrey
