Messages in this thread |  | | Date | Thu, 14 Jul 2016 08:49:56 +0200 | From | Peter Zijlstra <> | Subject | Re: Severe performance regression w/ 4.4+ on Android due to cgroup locking changes |
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On Wed, Jul 13, 2016 at 06:01:28PM -0400, Tejun Heo wrote:
> Technically, I think the lglock approach would be better here given > the combination of requirements; however, it's quite a bit more code > which would likely require some sophistications down the line (like > blocking new readers first at the start of down_write).
So the immediate problem with lg style locks is that the 'local' lock will not stay local since these are preemptible locks we can get migrations etc..
All fixable, but still.
> If we have to > go there, we'll go there but for now I think it'd be simpler to > conditionally switch to the expedited operations. It can be a config > option which is selected by !RT as you suggested. If anyone hits an > actual issue with that, we can go for the lglock thing.
So the main objection I have is that this isn't a fundamental fix, this only cures things because Android only runs on small machines.
If someone with a big computer tries to do the same things we're up some creek without no paddle. There's just no way we can make a global writer 'fast'.
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