Re: PCID review?

[Mel Gorman <mgorman@techsingularity.net>]

On Fri, Feb 10, 2017 at 02:07:19PM -0800, Andy Lutomirski wrote:
> > Ok, probably for the best albeit that is based on an inability to figure
> > out how it could be done efficiently and a suspicion that if it could be
> > done, the scheduler would be doing it already.
> >
> 
> FWIW, I am doing a bit of this.  For remote CPUs that aren't currently
> running a given mm, I just bump a per-mm generation count so that they
> know to flush next time around in switch_mm().  I'll need to add a new
> hook to the batched flush code to get this right, and I'll cc you on
> that.  Stay tuned.
> 

Ok, thanks.

> > [1] I could be completely wrong, I'm basing this on how people have
> >     behaved in the past during TLB-flush related discussions. They
> >     might have changed their mind.
> 
> We'll see.  The main benchmark that I'm relying on (so far) is that
> context switches get way faster, just ping ponging back and forth.  I
> suspect that the TLB refill cost is only a small part.
> 

Note that such a benchmark is not going to measure the TLB flush cost.
In itself, this is not bad but I suspect that the applications that care
about interference from TLB flushes by unrelated processes are not
applications that are context-switch intensive.

-- 
Mel Gorman
SUSE Labs

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