Re: [PATCH 11/20] Inline get_page_from_freelist() in the fast-path

Nick Piggin
2009-02-24T14:08:56Z

On Wednesday 25 February 2009 00:32:53 Mel Gorman wrote:
> On Tue, Feb 24, 2009 at 02:32:37AM +1100, Nick Piggin wrote:
> > On Monday 23 February 2009 10:17:20 Mel Gorman wrote:
> > > In the best-case scenario, use an inlined version of
> > > get_page_from_freelist(). This increases the size of the text but
> > > avoids time spent pushing arguments onto the stack.
> >
> > I'm quite fond of inlining ;) But it can increase register pressure as
> > well as icache footprint as well. x86-64 isn't spilling a lot more
> > registers to stack after these changes, is it?
>
> I didn't actually check that closely so I don't know for sure. Is there a
> handier way of figuring it out than eyeballing the assembly? In the end

I guess the 5 second check is to look at how much stack the function
uses. OTOH I think gcc does do a reasonable job at register allocation.

> I dropped the inline of this function anyway. It means the patches
> reduce rather than increase text size which is a bit more clear-cut.

Cool, clear cut patches for round 1 should help to get things moving.

> > In which case you will get extra icache footprint. What speedup does
> > it give in the cache-hot microbenchmark case?
>
> I wasn't measuring with a microbenchmark at the time of writing so I don't
> know. I was going entirely by profile counts running kernbench and the
> time spent running the benchmark.

OK. Well seeing as you have dropped this for the moment, let's not
dwell on it ;)