Re: [PATCH v2 2/2] powerpc32: optimise csum_partial() loop

[leroy christophe]

Le 17/08/2015 13:00, leroy christophe a Ãcrit :
> Le 17/08/2015 12:56, leroy christophe a Ãcrit :
> > Le 07/08/2015 01:25, Segher Boessenkool a Ãcrit :
> > > On Thu, Aug 06, 2015 at 05:45:45PM -0500, Scott Wood wrote:
> > > > If this makes performance non-negligibly worse on other 32-bit 
> > > > chips, and is
> > > > an important improvement on 8xx, then we can use an ifdef since 8xx 
> > > > already
> > > > requires its own kernel build.  I'd prefer to see a benchmark 
> > > > showing that it
> > > > actually does make things worse on those chips, though.
> > > And I'd like to see a benchmark that shows it *does not* hurt 
> > > performance
> > > on most chips, and does improve things on 8xx, and by how much. But it
> > > isn't *me* who has to show that, it is not my patch.
> > Ok, following this discussion I made some additional measurement and 
> > it looks like:
> > * There is almost no change on the 885
> > * There is a non negligeable degradation on the 8323 (19.5 tb ticks 
> > instead of 15.3)
> >
> > Thanks for pointing this out, I think my patch is therefore not good.
> Oops, I was talking about my other past, the one that was to optimise 
> ip_csum_fast.
> I still have to measure csum_partial
Now, I have the results for csum_partial(). The measurement is done with 
mftbl() before and after calling the function, with IRQ off to get a 
stable measure. Measurement is done with a transfer of vmlinux file done 
3 times via scp toward the target. We get approximatly 50000 calls to 
csum_partial()

On MPC885:
1/ Without the patchset, mean time spent in csum_partial() is 167 tb ticks.
2/ With the patchset, mean time is 150 tb ticks

On MPC8323:
1/ Without the patchset, mean time is 287 tb ticks
2/ With the patchset, mean time is 256 tb ticks

The improvement is approximatly 10% in both cases

So, unlike my patch on ip_fast_csum(), this one is worth it.

Christophe
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