Messages in this thread | | | Date | Wed, 11 Oct 2023 12:05:26 +0200 | From | Peter Zijlstra <> | Subject | Re: Re: [PATCH 01/15] sched/fair: Add avg_vruntime |
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On Wed, Oct 11, 2023 at 11:45:39AM +0200, Peter Zijlstra wrote: > On Wed, Oct 11, 2023 at 04:30:26PM +0800, Abel Wu wrote: > > On 10/11/23 3:30 PM, Peter Zijlstra Wrote: > > > On Wed, Oct 11, 2023 at 12:15:28PM +0800, Abel Wu wrote: > > > > On 5/31/23 7:58 PM, Peter Zijlstra wrote: > > > > > +/* > > > > > + * Compute virtual time from the per-task service numbers: > > > > > + * > > > > > + * Fair schedulers conserve lag: > > > > > + * > > > > > + * \Sum lag_i = 0 > > > > > + * > > > > > + * Where lag_i is given by: > > > > > + * > > > > > + * lag_i = S - s_i = w_i * (V - v_i) > > > > > > > > Since the ideal service time S is task-specific, should this be: > > > > > > > > lag_i = S_i - s_i = w_i * (V - v_i) > > > > > > It is not, S is the same for all tasks. Remember, the base form is a > > > differential equation and all tasks progress at the same time at dt/w_i > > > while S progresses at dt/W. > > > > IIUC it's V progresses at dt/W and is same for all tasks, not S which is > > measured in real time (V*w_i). > > Clearly I should wake up before replying ;-) > > V = S/W, so dV = dt/W and dS = dt > > Anyway, the point is that both V and S are the same across all tasks, > all tasks execute in parallel with infinitely small time increments. > > In reality this can't work ofc, so we get the approximations v_i and s_i > and lag is the deviation from the ideal.
Ah, I think I see. I'm making a mess of things aren't I.
I've got to run some errands, but I'll try and reply more coherently after.
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