Messages in this thread Patch in this message | | | Date | Mon, 20 Sep 2010 12:02:49 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH] sched: START_NICE feature (temporarily niced forks) (v3) |
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* Peter Zijlstra (peterz@infradead.org) wrote: > On Tue, 2010-09-14 at 16:25 -0400, Mathieu Desnoyers wrote: > > > > Index: linux-2.6-lttng.git/include/linux/sched.h > > =================================================================== > > --- linux-2.6-lttng.git.orig/include/linux/sched.h > > +++ linux-2.6-lttng.git/include/linux/sched.h > > @@ -1132,6 +1132,8 @@ struct sched_entity { > > u64 prev_sum_exec_runtime; > > > > u64 nr_migrations; > > + u64 fork_nice_timeout; > > + unsigned int fork_nice_penality; > > > > #ifdef CONFIG_SCHEDSTATS > > struct sched_statistics statistics; > > Index: linux-2.6-lttng.git/kernel/sched.c > > =================================================================== > > --- linux-2.6-lttng.git.orig/kernel/sched.c > > +++ linux-2.6-lttng.git/kernel/sched.c > > @@ -2421,6 +2421,8 @@ static void __sched_fork(struct task_str > > p->se.sum_exec_runtime = 0; > > p->se.prev_sum_exec_runtime = 0; > > p->se.nr_migrations = 0; > > + p->se.fork_nice_timeout = 0; > > + p->se.fork_nice_penality = 0; > > > > #ifdef CONFIG_SCHEDSTATS > > memset(&p->se.statistics, 0, sizeof(p->se.statistics)); > > Index: linux-2.6-lttng.git/kernel/sched_fair.c > > =================================================================== > > --- linux-2.6-lttng.git.orig/kernel/sched_fair.c > > +++ linux-2.6-lttng.git/kernel/sched_fair.c > > @@ -433,6 +433,14 @@ calc_delta_fair(unsigned long delta, str > > if (unlikely(se->load.weight != NICE_0_LOAD)) > > delta = calc_delta_mine(delta, NICE_0_LOAD, &se->load); > > > > + if (se->fork_nice_penality) { > > + delta <<= se->fork_nice_penality; > > + if ((s64)(se->sum_exec_runtime - se->fork_nice_timeout) > 0) { > > + se->fork_nice_penality = 0; > > + se->fork_nice_timeout = 0; > > + } > > + } > > + > > return delta; > > } > > Something like this ought to live at every place where you use se->load, > including sched_slice(), possibly wakeup_gran(), although that's more > heuristic, so you could possibly leave it out there.
Agreed for wakeup_gran(). I'll just remove the duplicate "if (unlikely(se->load.weight != NICE_0_LOAD))" check.
For sched_slice(), I don't know. sched_vslice() is used to take nice level into account when placing new tasks. sched_slice() takes only the weight into account, not the nice level. So given that I want to mimic the nice level impact, I'm not sure we have to take this into account at the sched_slice level.
Also, I wonder if leaving it out of account_entity_enqueue/dequeue() calls to add_cfs_task_weight() and inc/dec_cpu_load is OK ? Because it can be a pain to reequilibrate the cpu and task weights when the timeout occurs. The temporary effect of this nice-on-fork is to make the tasks a little lighter, so the weight is not accurate. But I wonder if we really care that much about it.
> > > @@ -832,6 +840,11 @@ dequeue_entity(struct cfs_rq *cfs_rq, st > > */ > > if (!(flags & DEQUEUE_SLEEP)) > > se->vruntime -= cfs_rq->min_vruntime; > > + > > + if (se->fork_nice_penality) { > > + se->fork_nice_penality = 0; > > + se->fork_nice_timeout = 0; > > + } > > } > > > > /* > > So you want to reset this penalty on each de-schedule, not only sleep > (but also preemptions)?
only sleeps. So I should put this within a
if (flags & DEQUEUE_SLEEP) { ... }
I suppose ?
> > > @@ -3544,8 +3557,27 @@ static void task_fork_fair(struct task_s > > > > update_curr(cfs_rq); > > > > - if (curr) > > + if (curr) { > > se->vruntime = curr->vruntime; > > + if (sched_feat(START_NICE)) { > > + if (curr->fork_nice_penality && > > + (s64)(curr->sum_exec_runtime > > + - curr->fork_nice_timeout) > 0) { > > + curr->fork_nice_penality = 0; > > + curr->fork_nice_timeout = 0; > > + } > > + > > + if (!curr->fork_nice_timeout) > > + curr->fork_nice_timeout = > > + curr->sum_exec_runtime; > > + curr->fork_nice_timeout += sched_slice(cfs_rq, curr); > > + curr->fork_nice_penality = min_t(unsigned int, > > + curr->fork_nice_penality + 1, 8); > > + se->fork_nice_timeout = curr->fork_nice_timeout > > + - curr->sum_exec_runtime; > > + se->fork_nice_penality = curr->fork_nice_penality; > > + } > > + } > > place_entity(cfs_rq, se, 1); > > > > if (sysctl_sched_child_runs_first && curr && entity_before(curr, se)) { > > If you stick than in a separate function you can loose 2 indent levels, > which would help with readability.
Excellent point, will do! That will let me add more comments into the function too.
Thanks a lot!
Mathieu
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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