Messages in this thread | | | Date | Mon, 27 Feb 2006 20:17:47 +1100 | From | Nick Piggin <> | Subject | Re: [Patch 2/7] Add sysctl for schedstats |
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Shailabh Nagar wrote: > schedstats-sysctl.patch > > Add sysctl option for controlling schedstats collection > dynamically. Delay accounting leverages schedstats for > cpu delay statistics. >
I'd sort of rather not tie this in with schedstats if possible. Schedstats adds a reasonable amount of cache footprint and branches in hot paths. Most of schedstats stuff is something that hardly anyone will use.
Sure you can share common code though...
> > Index: linux-2.6.16-rc4/kernel/sched.c > =================================================================== > --- linux-2.6.16-rc4.orig/kernel/sched.c 2006-02-27 01:20:04.000000000 -0500 > +++ linux-2.6.16-rc4/kernel/sched.c 2006-02-27 01:52:52.000000000 -0500 > @@ -382,11 +382,56 @@ static inline void task_rq_unlock(runque > } > > #ifdef CONFIG_SCHEDSTATS > + > +int schedstats_sysctl = 0; /* schedstats turned off by default */
Should be read mostly.
> +static DEFINE_PER_CPU(int, schedstats) = 0; > +
When the above is in the read mostly section, you won't need this at all.
You don't intend to switch the sysctl with great frequency, do you?
> +static void schedstats_set(int val) > +{ > + int i; > + static spinlock_t schedstats_lock = SPIN_LOCK_UNLOCKED; > + > + spin_lock(&schedstats_lock); > + schedstats_sysctl = val; > + for (i = 0; i < NR_CPUS; i++) > + per_cpu(schedstats, i) = val; > + spin_unlock(&schedstats_lock); > +} > + > +static int __init schedstats_setup_enable(char *str) > +{ > + schedstats_sysctl = 1; > + schedstats_set(schedstats_sysctl); > + return 1; > +} > + > +__setup("schedstats", schedstats_setup_enable); > + > +int schedstats_sysctl_handler(ctl_table *table, int write, struct file *filp, > + void __user *buffer, size_t *lenp, loff_t *ppos) > +{ > + int ret, prev = schedstats_sysctl; > + struct task_struct *g, *t; > + > + ret = proc_dointvec(table, write, filp, buffer, lenp, ppos); > + if ((ret != 0) || (prev == schedstats_sysctl)) > + return ret; > + if (schedstats_sysctl) { > + read_lock(&tasklist_lock); > + do_each_thread(g, t) { > + memset(&t->sched_info, 0, sizeof(t->sched_info)); > + } while_each_thread(g, t); > + read_unlock(&tasklist_lock); > + } > + schedstats_set(schedstats_sysctl);
You don't clear the rq's schedstats stuff here.
And clearing this at all is not really needed for the schedstats interface. You have a timestamp and a set of accumulated values, so it is easy to work out deltas. So do you need this?
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