Messages in this thread | | | Date | Thu, 30 Aug 2007 13:49:31 +0400 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2.6.21] Return available first timeslice to the creator, not parent |
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On 08/30, Peter Zijlstra wrote: > > On Thu, 2007-08-30 at 09:50 +0200, Vitaly Mayatskikh wrote: > > Short-living process returns its timeslice to the parent, this affects > > process that creates a lot of such short-living threads, because its > > not a parent for new threads. Patch fixes this issue and doesn't break > > kabi as does the patch from reporter: http://lkml.org/lkml/2007/4/7/21 > > > plain text document attachment (2.6.21-timeslice.patch), "proposed > > patch" > > diff -up -bB ./include/linux/sched.h.orig ./include/linux/sched.h > > --- ./include/linux/sched.h.orig 2007-08-21 09:20:22.000000000 +0200 > > +++ ./include/linux/sched.h 2007-08-27 10:14:06.000000000 +0200 > > @@ -827,7 +827,9 @@ struct task_struct { > > > > unsigned long policy; > > cpumask_t cpus_allowed; > > - unsigned int time_slice, first_time_slice; > > + unsigned int time_slice; > > + /* Pid of creator */ > > + unsigned int cpid; > > might as well make that pid_t, or maybe even a struct pid* and keep a > reference on it - the struct pid police might have an opinion.
I agree, "struct pid*" is better, because
1. we don't need a costly find_pid() in sched_exit() 2. we don't suffer from pid re-use problem
> > void fastcall sched_exit(struct task_struct *p) > > { > > unsigned long flags; > > struct rq *rq; > > - > > + struct task_struct* creator = NULL; > > /* > > * If the child was a (relative-) CPU hog then decrease > > - * the sleep_avg of the parent as well. > > + * the sleep_avg of the creator as well. > > */ > > - rq = task_rq_lock(p->parent, &flags); > > - if (p->first_time_slice && task_cpu(p) == task_cpu(p->parent)) { > > - p->parent->time_slice += p->time_slice; > > - if (unlikely(p->parent->time_slice > task_timeslice(p))) > > - p->parent->time_slice = task_timeslice(p); > > + if (p->cpid) { > > + struct pid *pid = find_get_pid((pid_t)p->cpid); > > + if (pid) { > > + creator = get_pid_task(pid, PIDTYPE_PID); > > + put_pid(pid);
sched_exit() was removed in 2.6.23-rc.
If you are going to re-introduce this logic, please don't do sched_exit() from release_task(). It was done this way just because we can't access ->parent after release_task(). But release_task() is called either too early, or too late for timeslice accounting, depending on ->exit_signal == -1.
I'd suggest to do this in do_exit(), before the last schedule(). Without write_unlock_irq() the code above needs a couple of rcu_read_lock()'s.
I am not sure Ingo will like this change though...
Oleg.
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