Re: [RFC][PATCH 00/16] sched: Core scheduling

Subhra Mazumdar
2019-02-21T18:47:13Z

On 2/21/19 6:03 AM, Peter Zijlstra wrote:
> On Wed, Feb 20, 2019 at 06:53:08PM -0800, Subhra Mazumdar wrote:
>> On 2/18/19 9:49 AM, Linus Torvalds wrote:
>>> On Mon, Feb 18, 2019 at 9:40 AM Peter Zijlstra <peterz@infradead.org> wrote:
>>>> However; whichever way around you turn this cookie; it is expensive and nasty.
>>> Do you (or anybody else) have numbers for real loads?
>>>
>>> Because performance is all that matters. If performance is bad, then
>>> it's pointless, since just turning off SMT is the answer.
>>>
>>> Linus
>> I tested 2 Oracle DB instances running OLTP on a 2 socket 44 cores system.
>> This is on baremetal, no virtualization.
> I'm thinking oracle schedules quite a bit, right? Then you get massive
> overhead (as shown).
Yes. In terms of idleness we have:

Users baseline core_sched
16    67% 70%
24    53% 59%
32    41% 49%

So there is more idleness with core sched which is understandable as there
can be forced idleness. The other part contributing to regression is most
likely overhead.
>
> The thing with virt workloads is that if they don't VMEXIT lots, they
> also don't schedule lots (the vCPU stays running, nested scheduler
> etc..).
I plan to run some VM workloads.
>
> Also; like I wrote, it is quite possible there is some sibling rivalry
> here, which can cause excessive rescheduling. Someone would have to
> trace a workload and check.
>
> My older patches had a condition that would not preempt a task for a
> little while, such that it might make _some_ progress, these patches
> don't have that (yet).
>