On Wed, Jan 08, 2014 at 01:59:30PM -0800, Andrew Morton wrote:
> On Wed, 8 Jan 2014 23:37:49 +0200 Pekka Enberg <penberg@xxxxxxxxxx> wrote:
>
> > The patch looks good to me but it probably should go through Andrew's tree.
>
> yup.
>
> page_mapping() will be called quite frequently, and adding a new
> test-n-branch in there will be somewhat costly. We might end up with a
> better kernel if we were to instead revert 8456a648cf44f. How useful
> was that patch?
Hello,
Performance effect of this patch was decribed in the cover-letter, but
I missed to attach it to patch description. Sorry about that.
In summary, this patch saves some memory and decreases cache-footprint
so that it increases performance.
Here goes the description in cover-letter.
Below is some numbers of 'cat /proc/slabinfo'.
* Before *
# name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables [snip...]
kmalloc-512 527 600 512 8 1 : tunables 54 27 0 : slabdata 75 75 0
kmalloc-256 210 210 256 15 1 : tunables 120 60 0 : slabdata 14 14 0
kmalloc-192 1040 1040 192 20 1 : tunables 120 60 0 : slabdata 52 52 0
kmalloc-96 750 750 128 30 1 : tunables 120 60 0 : slabdata 25 25 0
kmalloc-64 2773 2773 64 59 1 : tunables 120 60 0 : slabdata 47 47 0
kmalloc-128 660 690 128 30 1 : tunables 120 60 0 : slabdata 23 23 0
kmalloc-32 11200 11200 32 112 1 : tunables 120 60 0 : slabdata 100 100 0
kmem_cache 197 200 192 20 1 : tunables 120 60 0 : slabdata 10 10 0
* After *
# name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables [snip...]
kmalloc-512 525 640 512 8 1 : tunables 54 27 0 : slabdata 80 80 0
kmalloc-256 210 210 256 15 1 : tunables 120 60 0 : slabdata 14 14 0
kmalloc-192 1016 1040 192 20 1 : tunables 120 60 0 : slabdata 52 52 0
kmalloc-96 560 620 128 31 1 : tunables 120 60 0 : slabdata 20 20 0
kmalloc-64 2148 2280 64 60 1 : tunables 120 60 0 : slabdata 38 38 0
kmalloc-128 647 682 128 31 1 : tunables 120 60 0 : slabdata 22 22 0
kmalloc-32 11360 11413 32 113 1 : tunables 120 60 0 : slabdata 101 101 0
kmem_cache 197 200 192 20 1 : tunables 120 60 0 : slabdata 10 10 0
kmem_caches consisting of objects less than or equal to 128 byte have one more
objects in a slab. You can see it at objperslab.
Here are the performance results on my 4 cpus machine.
* Before *
Performance counter stats for 'perf bench sched messaging -g 50 -l 1000' (10 runs):
238,309,671 cache-misses ( +- 0.40% )
12.010172090 seconds time elapsed ( +- 0.21% )
* After *
Performance counter stats for 'perf bench sched messaging -g 50 -l 1000' (10 runs):
229,945,138 cache-misses ( +- 0.23% )
11.627897174 seconds time elapsed ( +- 0.14% )
cache-misses are reduced by this patchset, roughly 5%.
And elapsed times are also improved by 3.1% to baseline.
Thanks.
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