Messages in this thread Patch in this message | | | Date | Mon, 27 Feb 2006 09:52:03 +0100 | From | Ingo Molnar <> | Subject | Re: [Patch 2/7] Add sysctl for schedstats |
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the principle looks OK to me, just a few minor nits:
> #ifdef CONFIG_SCHEDSTATS > + > +int schedstats_sysctl = 0; /* schedstats turned off by default */
no need to initialize to 0.
> +static DEFINE_PER_CPU(int, schedstats) = 0;
ditto.
> + > +static void schedstats_set(int val) > +{ > + int i; > + static spinlock_t schedstats_lock = SPIN_LOCK_UNLOCKED;
move spinlock out of the function and use DEFINE_SPINLOCK. (But ... see below for suggestion to get rid of this lock altogether.)
> + 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);
why not just introduce a schedstats_lock mutex, and acquire it for both the 'if (schedstats_sysctl)' line and the schedstats_set() line. That will make the locking meaningful: two parallel sysctl ops will be atomic to each other. [right now they wont be and they can clear schedstat data in parallel -> not a big problem but it makes schedstats_lock rather meaningless]
> -#define SCHEDSTAT_VERSION 12 > +#define SCHEDSTAT_VERSION 13 > > static int show_schedstat(struct seq_file *seq, void *v) > { > @@ -394,6 +439,10 @@ static int show_schedstat(struct seq_fil > > seq_printf(seq, "version %d\n", SCHEDSTAT_VERSION); > seq_printf(seq, "timestamp %lu\n", jiffies); > + if (!schedstats_sysctl) { > + seq_printf(seq, "State Off\n"); > + return 0; > + }
and show_schedstat() should then also take the schedstats_lock mutex.
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