Re: [GIT PULL] Re: REGRESSION: Performance regressions fromswitching anon_vma->lock to mutex

From: Benjamin Herrenschmidt
Date: Thu Jun 16 2011 - 18:24:10 EST

On Thu, 2011-06-16 at 22:25 +0200, Ingo Molnar wrote:

> > Whatever does the boosting will need to have process context and
> > can be subject to delays, so that pretty much needs to be a
> > kthread. But it will context-switch quite rarely, so should not be
> > a problem.
> So user-return notifiers ought to be the ideal platform for that,
> right? We don't even have to touch the scheduler: anything that
> schedules will eventually return to user-space, at which point the
> RCU GC magic can run.
> And user-return-notifiers can be triggered from IRQs as well.
> That allows us to get rid of softirqs altogether and maybe even speed
> the whole thing up and allow it to be isolated better.

I'm a little worried of relying on things returning to userspace.

One could imagine something like a router appliance where userspace is
essentially asleep forever and everything happens in the kernel
(networking via softirq, maybe NFS kernel server, ...)


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