On Mon, Aug 19, 2013 at 06:01:02PM +0200, Peter Zijlstra wrote:
> +static inline void init_sd_lb_stats(struct sd_lb_stats *sds)
> +{
> + /*
> + * struct sd_lb_stats {
> + * struct sched_group * busiest; // 0 8
> + * struct sched_group * this; // 8 8
> + * long unsigned int total_load; // 16 8
> + * long unsigned int total_pwr; // 24 8
> + * long unsigned int avg_load; // 32 8
> + * struct sg_lb_stats {
> + * long unsigned int avg_load; // 40 8
> + * long unsigned int group_load; // 48 8
> + * ...
> + * } busiest_stat; // 40 56
> + * struct sg_lb_stats this_stat; // 96 56
> + *
> + * // size: 152, cachelines: 3, members: 7
> + * // last cacheline: 24 bytes
> + * };
> + *
> + * Skimp on the clearing to avoid duplicate work. We can avoid clearing
> + * this_stat because update_sg_lb_stats() does a full clear/assignment.
> + * We must however clear busiest_stat::avg_load because
> + * update_sd_pick_busiest() reads this before assignment.
> + */
> + memset(sds, 0, offsetof(struct sd_lb_stats, busiest_stat.group_load));
Hello, Peter.
IMHO, this is so tricky.
With below change, we can simply do 'offsetof(struct sd_lb_stats,
busiest_stat)'.
@@ -4546,7 +4546,7 @@ static bool update_sd_pick_busiest(struct lb_env *env,
struct sched_group *sg,
struct sg_lb_stats *sgs)
{
- if (sgs->avg_load <= sds->busiest_stat.avg_load)
+ if (!sds->busiest && sgs->avg_load <= sds->busiest_stat.avg_load)
return false;
if (sgs->sum_nr_running > sgs->group_capacity)
Thanks.
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