[RFC PATCH 0/5] powerpc/mm/slice: improve slice speed and stack use

[Nicholas Piggin]

On Mon, 12 Feb 2018 16:02:23 +0100
Christophe LEROY <christophe.leroy at c-s.fr> wrote:

> Le 10/02/2018 à 09:11, Nicholas Piggin a écrit :
> > This series intends to improve performance and reduce stack
> > consumption in the slice allocation code. It does it by keeping slice
> > masks in the mm_context rather than compute them for each allocation,
> > and by reducing bitmaps and slice_masks from stacks, using pointers
> > instead where possible.
> > 
> > checkstack.pl gives, before:
> > 0x00000de4 slice_get_unmapped_area [slice.o]:           656
> > 0x00001b4c is_hugepage_only_range [slice.o]:            512
> > 0x0000075c slice_find_area_topdown [slice.o]:           416
> > 0x000004c8 slice_find_area_bottomup.isra.1 [slice.o]:   272
> > 0x00001aa0 slice_set_range_psize [slice.o]:             240
> > 0x00000a64 slice_find_area [slice.o]:                   176
> > 0x00000174 slice_check_fit [slice.o]:                   112
> > 
> > after:
> > 0x00000d70 slice_get_unmapped_area [slice.o]:           320
> > 0x000008f8 slice_find_area [slice.o]:                   144
> > 0x00001860 slice_set_range_psize [slice.o]:             144
> > 0x000018ec is_hugepage_only_range [slice.o]:            144
> > 0x00000750 slice_find_area_bottomup.isra.4 [slice.o]:   128
> > 
> > The benchmark in https://github.com/linuxppc/linux/issues/49 gives, before:
> > $ time ./slicemask
> > real	0m20.712s
> > user	0m5.830s
> > sys	0m15.105s
> > 
> > after:
> > $ time ./slicemask
> > real	0m13.197s
> > user	0m5.409s
> > sys	0m7.779s  
> 
> Hi,
> 
> I tested your serie on an 8xx, on top of patch 
> https://patchwork.ozlabs.org/patch/871675/
> 
> I don't get a result as significant as yours, but there is some 
> improvment anyway:
> 
> ITERATION 500000
> 
> Before:
> 
> root at vgoip:~# time ./slicemask
> real    0m 33.26s
> user    0m 1.94s
> sys     0m 30.85s
> 
> After:
> root at vgoip:~# time ./slicemask
> real    0m 29.69s
> user    0m 2.11s
> sys     0m 27.15s
> 
> Most significant improvment is obtained with the first patch of your serie:
> root at vgoip:~# time ./slicemask
> real    0m 30.85s
> user    0m 1.80s
> sys     0m 28.57s

Okay, thanks. Are you still spending significant time in the slice
code?

> 
> Had to modify your serie a bit, if you are interested I can post it.
> 

Sure, that would be good.

Thanks,
Nick