Re: [PATCH] slub: prefetch next freelist pointer in slab_alloc()

From: Eric Dumazet
Date: Fri Dec 16 2011 - 12:18:46 EST


Le vendredi 16 dÃcembre 2011 Ã 10:31 -0600, Christoph Lameter a Ãcrit :
> On Fri, 16 Dec 2011, Eric Dumazet wrote:
>
> > Recycling a page is a problem, since freelist link chain is hot on
> > cpu(s) which freed objects, and possibly very cold on cpu currently
> > owning slab.
>
> Good idea. How do the tcp benchmarks look after this?
>
> Looks sane.
>
> Acked-by: Christoph Lameter <cl@xxxxxxxxx>

Thanks !

I wouldnt expect TCP being a huge win (most of cpu is consumed in tcp
stack, not really memory allocations), but still...

[I expect much better gain on an UDP load, where memory allocator costs
are higher ]

$ cat netperf.sh
for in in `seq 1 32`
do
netperf -H 192.168.20.110 -v 0 -l -100000 -t TCP_RR &
done
wait

If cpu0 handles network interrupts, and other cpus run applications :

Before

Performance counter stats for './netperf.sh':

38001,927957 task-clock # 2,344 CPUs utilized
3 306 138 context-switches # 0,087 M/sec
79 CPU-migrations # 0,000 M/sec
9 656 page-faults # 0,000 M/sec
83 564 329 446 cycles # 2,199 GHz
61 350 744 867 stalled-cycles-frontend # 73,42% frontend cycles idle
34 907 541 687 stalled-cycles-backend # 41,77% backend cycles idle
44 739 971 752 instructions # 0,54 insns per cycle
# 1,37 stalled cycles per insn
8 662 005 669 branches # 227,936 M/sec
249 555 153 branch-misses # 2,88% of all branches

16,214220448 seconds time elapsed

After :

Performance counter stats for './netperf.sh':

37035,347847 task-clock # 2,374 CPUs utilized
3 314 540 context-switches # 0,089 M/sec
131 CPU-migrations # 0,000 M/sec
9 691 page-faults # 0,000 M/sec
81 783 678 294 cycles # 2,208 GHz
59 595 242 695 stalled-cycles-frontend # 72,87% frontend cycles idle
34 367 813 304 stalled-cycles-backend # 42,02% backend cycles idle
44 698 853 546 instructions # 0,55 insns per cycle
# 1,33 stalled cycles per insn
8 654 940 308 branches # 233,694 M/sec
245 578 562 branch-misses # 2,84% of all branches

15,597940419 seconds time elapsed


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