On Tue 30-05-23 11:52:38, Marcelo Tosatti wrote:
> The interruption caused by queueing work on nohz_full CPUs
> is undesirable for certain aplications.
>
> Fix by not refreshing per-CPU stats of nohz_full CPUs.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
>
> ---
>
> Index: linux-vmstat-remote/mm/vmstat.c
> ===================================================================
> --- linux-vmstat-remote.orig/mm/vmstat.c
> +++ linux-vmstat-remote/mm/vmstat.c
> @@ -1877,12 +1877,31 @@ static void refresh_vm_stats(struct work
> refresh_cpu_vm_stats(true);
> }
>
> +#ifdef CONFIG_NO_HZ_FULL
> +static inline const cpumask_t *tickless_cpumask(void)
> +{
> + return tick_nohz_full_mask;
> +}
> +#else
> +static cpumask_t empty_cpumask;
> +static inline const cpumask_t *tickless_cpumask(void)
> +{
> + return &empty_cpumask;
> +}
> +#endif
> +
> int vmstat_refresh(struct ctl_table *table, int write,
> void *buffer, size_t *lenp, loff_t *ppos)
> {
> long val;
> int err;
> int i;
> + cpumask_var_t dstmask;
> +
> + if (!alloc_cpumask_var(&dstmask, GFP_KERNEL))
> + return -ENOMEM;
> +
> + cpumask_andnot(dstmask, cpu_possible_mask, tickless_cpumask());
Similar feedback to the patch 2. wouldn't it make more sense to opencode
schedule_on_each_cpu here and use cpu_is_isolated instead?
>
> /*
> * The regular update, every sysctl_stat_interval, may come later
> @@ -1896,7 +1915,9 @@ int vmstat_refresh(struct ctl_table *tab
> * transiently negative values, report an error here if any of
> * the stats is negative, so we know to go looking for imbalance.
> */
> - err = schedule_on_each_cpu(refresh_vm_stats);
> + err = schedule_on_each_cpumask(refresh_vm_stats, dstmask);
> + free_cpumask_var(dstmask);
> +
> if (err)
> return err;
> for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
>
--
Michal Hocko
SUSE Labs
