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

[Nicholas Piggin]

On Mon, 12 Feb 2018 18:42:21 +0100
Christophe LEROY <christophe.leroy at c-s.fr> wrote:

> Le 12/02/2018 à 16:24, Nicholas Piggin a écrit :
> > 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?  
> 
> Do you mean am I still updating my patches ? No I hope we are at last 

Actually I was wondering about CPU time spent for the microbenchmark :)

> run with v4 now that Aneesh has tagged all of them as reviewed-by himself.
> Once the serie has been accepted, my next step will be to backport at 
> least the 3 first ones in kernel 4.14
> 
> >   
> >>
> >> Had to modify your serie a bit, if you are interested I can post it.
> >>  
> > 
> > Sure, that would be good.  
> 
> Ok, lets share it. The patch are not 100% clean.

Those look pretty good, thanks for doing that work.

Thanks,
Nick