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

[Christophe LEROY]

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 
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.

Christophe