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

[Subhra Mazumdar]

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?