Re: [PATCH] swap: remove the struct cpumask has_work

[Chris Metcalf]

On 7/31/2014 7:51 AM, Michal Hocko wrote:
> On Thu 31-07-14 11:30:19, Lai Jiangshan wrote:
> > It is suggested that cpumask_var_t and alloc_cpumask_var() should be used
> > instead of struct cpumask.  But I don't want to add this complicity nor
> > leave this unwelcome "static struct cpumask has_work;", so I just remove
> > it and use flush_work() to perform on all online drain_work.  flush_work()
> > performs very quickly on initialized but unused work item, thus we don't
> > need the struct cpumask has_work for performance.
> Why? Just because there is general recommendation for using
> cpumask_var_t rather than cpumask?
>
> In this particular case cpumask shouldn't matter much as it is static.
> Your code will work as well, but I do not see any strong reason to
> change it just to get rid of cpumask which is not on stack.

The code uses for_each_cpu with a cpumask to avoid waking cpus that don't
need to do work.  This is important for the nohz_full type functionality,
power efficiency, etc.  So, nack for this change.

--
Chris Metcalf, Tilera Corp.
http://www.tilera.com

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/