Re: [RFC PATCH v2 11/17] sched: Basic tracking of matching tasks

[Subhra Mazumdar]

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.