On Thu, 14 Aug 2008 04:17:32 pm Mark Nelson wrote:
> Hi All,
>
> What follows is an updated version of copy_4K_page that has been tuned
> for the Cell processor. With this new routine it was found that the
> system time measured when compiling a 2.6.26 pseries_defconfig was
> reduced by ~10s:
>
> mainline (2.6.27-rc1-00632-g2e1e921):
>
> real 17m8.727s
> user 59m48.693s
> sys 3m56.089s
>
> real 17m9.350s
> user 59m44.822s
> sys 3m56.666s
>
> new routine:
>
> real 17m7.311s
> user 59m51.339s
> sys 3m47.043s
>
> real 17m7.863s
> user 59m49.028s
> sys 3m46.608s
>
> This same routine was also found to improve performance on 970 CPUs
> too (but by a much smaller amount):
>
> mainline (2.6.27-rc1-00632-g2e1e921):
>
> real 16m8.545s
> user 14m38.134s
> sys 1m55.156s
>
> real 16m7.089s
> user 14m37.974s
> sys 1m55.010s
>
> new routine:
>
> real 16m11.641s
> user 14m37.251s
> sys 1m52.618s
>
> real 16m6.139s
> user 14m38.282s
> sys 1m53.184s
>
>
> I also did testing on Power{3..6} and I found that Power3, Power5 and
> Power6 did better with this new routine when the dcbt and dcbz
> weren't used (in which case they achieved performance comparable to
> the existing kernel copy_4K_page routine). Power4 on other hand
> performed slightly better with the dcbt and dcbz included (still
> comparable to the current kernel copy_4K_page).
>
> So in order to get the best performance across the board I created a
> new CPU feature that will govern whether the dcbt and dcbz are used
> (and un-creatively named it CPU_FTR_CP_USE_DCBTZ). I added it to the
> CPU features of Cell, Power4 and 970.
> Unfortunately I don't have access to a PA6T but judging by the
> marketing material I could find, it looks like it has a strong enough
> hardware prefetcher that it probably wouldn't benefit from the dcbt
> and dcbz...
>
> Okay, that's probably enough prattling along - you can all go and look
> at the code now.
>
> All comments appreciated
>
> [I decided to post the whole copy routine rather than a diff between
> it and the current one because I found the diff quite unreadable. I'll post
> a real patchset after I've addressed any comments.]
>
> Many thanks!
>
The actual patches for the new copy_4K_page() follow this.
Note: I changed the order of the patches so that the new CPU feature
bit is introduced in the first patch and then the new copy_4K_page
is introduced in the second patch.
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