Messages in this thread | | | Date | Fri, 1 Aug 2014 13:16:05 -0400 | From | Chris Metcalf <> | Subject | Re: [PATCH] swap: remove the struct cpumask has_work |
| |
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@tilera.com> if the change is taken.
-- Chris Metcalf, Tilera Corp. http://www.tilera.com
| |