On 7/31/2014 9:39 PM, Lai Jiangshan wrote:
On 08/01/2014 12:09 AM, Chris Metcalf wrote:
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.
flush_work() on initialized but unused work item just disables irq and
fetches work->data to test and restores irq and return.
the struct cpumask has_work is just premature optimization.
Yes, I see your point. I was mistakenly thinking that your patch resulted
in calling schedule_work() on all the online cpus.
Given that, I think your suggestion is reasonable, though like Michal,
I'm not sure it necessarily rises to the level of it being worth changing the
code at this point. Regardless, I withdraw my nack, and you can add my
Reviewed-by: Chris Metcalf <cmetcalf@xxxxxxxxxx> if the change is taken.
--
Chris Metcalf, Tilera Corp.
http://www.tilera.com
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