Messages in this thread |  | | Date | Tue, 24 Nov 2020 10:31:49 +1100 | From | Balbir Singh <> | Subject | Re: [PATCH -tip 09/32] sched/fair: Snapshot the min_vruntime of CPUs on force idle |
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On Mon, Nov 23, 2020 at 07:31:31AM -0500, Vineeth Pillai wrote: > Hi Balbir, > > On 11/22/20 6:44 AM, Balbir Singh wrote: > > > > This seems cumbersome, is there no way to track the min_vruntime via > > rq->core->min_vruntime? > Do you mean to have a core wide min_vruntime? We had a > similar approach from v3 to v7 and it had major issues which > broke the assumptions of cfs. There were some lengthy > discussions and Peter explained in-depth about the issues: > > https://lwn.net/ml/linux-kernel/20200506143506.GH5298@hirez.programming.kicks-ass.net/ > https://lwn.net/ml/linux-kernel/20200515103844.GG2978@hirez.programming.kicks-ass.net/ >
One of the equations in the link is
">From which immediately follows that:
T_k + T_l S_k+l = --------- (13) W_k + W_l
On which we can define a combined lag:
lag_k+l(i) := S_k+l - s_i (14)
And that gives us the tools to compare tasks across a combined runqueue. "
S_k+l reads like rq->core->vruntime, but it sounds like the equivalent of rq->core->vruntime is updated when we enter forced idle as opposed to all the time.
Balbir
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