From: Abel Wu <wuyun.abel@bytedance.com>
To: Peter Zijlstra <peterz@infradead.org>,
mingo@kernel.org, vincent.guittot@linaro.org
Cc: linux-kernel@vger.kernel.org, juri.lelli@redhat.com,
dietmar.eggemann@arm.com, rostedt@goodmis.org,
bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
corbet@lwn.net, qyousef@layalina.io, chris.hyser@oracle.com,
patrick.bellasi@matbug.net, pjt@google.com, pavel@ucw.cz,
qperret@google.com, tim.c.chen@linux.intel.com,
joshdon@google.com, timj@gnu.org, kprateek.nayak@amd.com,
yu.c.chen@intel.com, youssefesmat@chromium.org,
joel@joelfernandes.org, efault@gmx.de, tglx@linutronix.de
Subject: Re: [PATCH 01/15] sched/fair: Add avg_vruntime
Date: Wed, 11 Oct 2023 12:15:28 +0800 [thread overview]
Message-ID: <75adcb1a-c02f-4d7c-bd9c-ab4f403af3e8@bytedance.com> (raw)
In-Reply-To: <20230531124603.654144274@infradead.org>
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)
> + *
> + * Where S is the ideal service time and V is it's virtual time counterpart.
> + * Therefore:
> + *
> + * \Sum lag_i = 0
> + * \Sum w_i * (V - v_i) = 0
> + * \Sum w_i * V - w_i * v_i = 0
> + *
> + * From which we can solve an expression for V in v_i (which we have in
> + * se->vruntime):
> + *
> + * \Sum v_i * w_i \Sum v_i * w_i
> + * V = -------------- = --------------
> + * \Sum w_i W
> + *
> + * Specifically, this is the weighted average of all entity virtual runtimes.
> + *
> + * [[ NOTE: this is only equal to the ideal scheduler under the condition
> + * that join/leave operations happen at lag_i = 0, otherwise the
> + * virtual time has non-continguous motion equivalent to:
> + *
> + * V +-= lag_i / W
> + *
> + * Also see the comment in place_entity() that deals with this. ]]
> + *
> + * However, since v_i is u64, and the multiplcation could easily overflow
> + * transform it into a relative form that uses smaller quantities:
> + *
> + * Substitute: v_i == (v_i - v0) + v0
> + *
> + * \Sum ((v_i - v0) + v0) * w_i \Sum (v_i - v0) * w_i
> + * V = ---------------------------- = --------------------- + v0
> + * W W
> + *
> + * Which we track using:
> + *
> + * v0 := cfs_rq->min_vruntime
> + * \Sum (v_i - v0) * w_i := cfs_rq->avg_vruntime
IMHO 'sum_runtime' would be more appropriate? Since it actually is
the summed real time rather than virtual time. And also 'sum_load'
instead of 'avg_load'.
Thanks & Best,
Abel
next prev parent reply other threads:[~2023-10-11 4:21 UTC|newest]
Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-31 11:58 [PATCH 00/15] sched: EEVDF and latency-nice and/or slice-attr Peter Zijlstra
2023-05-31 11:58 ` [PATCH 01/15] sched/fair: Add avg_vruntime Peter Zijlstra
2023-06-02 13:51 ` Vincent Guittot
2023-06-02 14:27 ` Peter Zijlstra
2023-06-05 7:18 ` Vincent Guittot
2023-08-10 7:10 ` [tip: sched/core] sched/fair: Add cfs_rq::avg_vruntime tip-bot2 for Peter Zijlstra
2023-10-11 4:15 ` Abel Wu [this message]
2023-10-11 7:30 ` [PATCH 01/15] sched/fair: Add avg_vruntime Peter Zijlstra
2023-10-11 8:30 ` Abel Wu
2023-10-11 9:45 ` Peter Zijlstra
2023-10-11 10:05 ` Peter Zijlstra
2023-10-11 13:08 ` Peter Zijlstra
2023-05-31 11:58 ` [PATCH 02/15] sched/fair: Remove START_DEBIT Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] sched/fair: Remove sched_feat(START_DEBIT) tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 03/15] sched/fair: Add lag based placement Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2023-10-11 12:00 ` [PATCH 03/15] " Abel Wu
2023-10-11 13:24 ` Peter Zijlstra
2023-10-12 7:04 ` Abel Wu
2023-10-13 7:37 ` Peter Zijlstra
2023-10-13 8:14 ` Abel Wu
2023-10-12 19:15 ` Benjamin Segall
2023-10-12 22:34 ` Peter Zijlstra
2023-10-13 16:35 ` Peter Zijlstra
2023-10-14 8:08 ` Mike Galbraith
2023-10-13 14:34 ` Peter Zijlstra
2023-05-31 11:58 ` [PATCH 04/15] rbtree: Add rb_add_augmented_cached() helper Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 05/15] sched/fair: Implement an EEVDF like policy Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] sched/fair: Implement an EEVDF-like scheduling policy tip-bot2 for Peter Zijlstra
2023-09-29 21:40 ` [PATCH 05/15] sched/fair: Implement an EEVDF like policy Benjamin Segall
2023-10-02 17:39 ` Peter Zijlstra
2023-10-11 4:14 ` Abel Wu
2023-10-11 7:33 ` Peter Zijlstra
2023-10-11 11:49 ` Abel Wu
2023-09-30 0:09 ` [PATCH] sched/fair: fix pick_eevdf to always find the correct se Benjamin Segall
2023-10-03 10:42 ` [tip: sched/urgent] sched/fair: Fix pick_eevdf() tip-bot2 for Benjamin Segall
[not found] ` <CGME20231004203940eucas1p2f73b017497d1f4239a6e236fdb6019e2@eucas1p2.samsung.com>
2023-10-04 20:39 ` [PATCH] sched/fair: fix pick_eevdf to always find the correct se Marek Szyprowski
2023-10-09 7:53 ` [tip: sched/urgent] sched/eevdf: Fix pick_eevdf() tip-bot2 for Benjamin Segall
2023-10-11 12:12 ` [PATCH] sched/fair: fix pick_eevdf to always find the correct se Abel Wu
2023-10-11 13:14 ` Peter Zijlstra
2023-10-12 10:04 ` Abel Wu
2023-10-11 21:01 ` Benjamin Segall
2023-10-12 10:25 ` Abel Wu
2023-10-12 17:51 ` Benjamin Segall
2023-10-13 3:46 ` Abel Wu
2023-10-13 16:51 ` Benjamin Segall
2023-05-31 11:58 ` [PATCH 06/15] sched: Commit to lag based placement Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] sched/fair: " tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 07/15] sched/smp: Use lag to simplify cross-runqueue placement Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2023-09-12 15:32 ` [PATCH 07/15] " Sebastian Andrzej Siewior
2023-09-13 9:03 ` Peter Zijlstra
2023-10-04 1:17 ` [PATCH] sched/fair: Preserve PLACE_DEADLINE_INITIAL deadline Daniel Jordan
2023-10-04 13:09 ` [PATCH v2] " Daniel Jordan
2023-10-04 15:46 ` Chen Yu
2023-10-06 16:31 ` Daniel Jordan
2023-10-12 4:48 ` K Prateek Nayak
2023-10-05 5:56 ` [PATCH] " K Prateek Nayak
2023-10-06 16:35 ` Daniel Jordan
2023-10-06 16:48 ` [PATCH] sched/fair: Always update_curr() before placing at enqueue Daniel Jordan
2023-10-06 19:58 ` Peter Zijlstra
2023-10-18 0:43 ` Daniel Jordan
2023-10-16 5:39 ` K Prateek Nayak
2023-05-31 11:58 ` [PATCH 08/15] sched: Commit to EEVDF Peter Zijlstra
2023-06-16 21:23 ` Joel Fernandes
2023-06-22 12:01 ` Ingo Molnar
2023-06-22 13:11 ` Joel Fernandes
2023-08-10 7:10 ` [tip: sched/core] sched/fair: " tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 09/15] sched/debug: Rename min_granularity to base_slice Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] sched/debug: Rename sysctl_sched_min_granularity to sysctl_sched_base_slice tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 10/15] sched/fair: Propagate enqueue flags into place_entity() Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 11/15] sched/eevdf: Better handle mixed slice length Peter Zijlstra
2023-06-02 13:45 ` Vincent Guittot
2023-06-02 15:06 ` Peter Zijlstra
2023-06-10 6:34 ` Chen Yu
2023-06-10 11:22 ` Peter Zijlstra
2023-05-31 11:58 ` [RFC][PATCH 12/15] sched: Introduce latency-nice as a per-task attribute Peter Zijlstra
2023-05-31 11:58 ` [RFC][PATCH 13/15] sched/fair: Implement latency-nice Peter Zijlstra
2023-06-06 14:54 ` Vincent Guittot
2023-06-08 10:34 ` Peter Zijlstra
2023-06-08 12:44 ` Peter Zijlstra
2023-10-11 23:24 ` Benjamin Segall
2023-05-31 11:58 ` [RFC][PATCH 14/15] sched/fair: Add sched group latency support Peter Zijlstra
2023-05-31 11:58 ` [RFC][PATCH 15/15] sched/eevdf: Use sched_attr::sched_runtime to set request/slice Peter Zijlstra
2023-06-01 13:55 ` Vincent Guittot
2023-06-08 11:52 ` Peter Zijlstra
2023-08-24 0:52 ` [PATCH 00/15] sched: EEVDF and latency-nice and/or slice-attr Daniel Jordan
2023-09-06 13:13 ` Peter Zijlstra
2023-09-29 16:54 ` Youssef Esmat
2023-10-02 15:55 ` Youssef Esmat
2023-10-02 18:41 ` Peter Zijlstra
2023-10-05 12:05 ` Peter Zijlstra
2023-10-05 14:14 ` Peter Zijlstra
2023-10-05 14:42 ` Peter Zijlstra
2023-10-05 18:23 ` Youssef Esmat
2023-10-06 0:36 ` Youssef Esmat
2023-10-10 8:08 ` Peter Zijlstra
2023-10-07 22:04 ` Peter Zijlstra
2023-10-09 14:41 ` Peter Zijlstra
2023-10-10 0:51 ` Youssef Esmat
2023-10-10 8:01 ` Peter Zijlstra
2023-10-16 16:50 ` Peter Zijlstra
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