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SubjectRe: Re: [PATCH 01/15] sched/fair: Add avg_vruntime
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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).

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