Re: [rfc 00/18] slub: irqless/lockless slow allocation paths

[David Rientjes <rientjes@google.com>]

On Wed, 16 Nov 2011, Eric Dumazet wrote:

> > Adding SLUB_STATS gives :
> > 
> > $ cd /sys/kernel/slab/skbuff_head_cache ; grep . *
> > aliases:6
> > align:8
> > grep: alloc_calls: Function not implemented
> > alloc_fastpath:89181782 C0=89173048 C1=1599 C2=1357 C3=2140 C4=802 C5=675 C6=638 C7=1523
> > alloc_from_partial:412658 C0=412658
> > alloc_node_mismatch:0
> > alloc_refill:593417 C0=593189 C1=19 C2=15 C3=24 C4=51 C5=18 C6=17 C7=84
> > alloc_slab:2831313 C0=2831285 C1=2 C2=2 C3=2 C4=2 C5=12 C6=4 C7=4
> > alloc_slowpath:4430371 C0=4430112 C1=20 C2=17 C3=25 C4=57 C5=31 C6=21 C7=88
> > cache_dma:0
> > cmpxchg_double_cpu_fail:0
> > cmpxchg_double_fail:1 C0=1
> > cpu_partial:30
> > cpu_partial_alloc:592991 C0=592981 C2=1 C4=5 C5=2 C6=1 C7=1
> > cpu_partial_free:4429836 C0=592981 C1=25 C2=19 C3=23 C4=3836767 C5=6 C6=8 C7=7
> > cpuslab_flush:0
> > cpu_slabs:107
> > deactivate_bypass:3836954 C0=3836923 C1=1 C2=2 C3=1 C4=6 C5=13 C6=4 C7=4
> > deactivate_empty:2831168 C4=2831168
> > deactivate_full:0
> > deactivate_remote_frees:0
> > deactivate_to_head:0
> > deactivate_to_tail:0
> > destroy_by_rcu:0
> > free_add_partial:0
> > grep: free_calls: Function not implemented
> > free_fastpath:21192924 C0=21186268 C1=1420 C2=1204 C3=1966 C4=572 C5=349 C6=380 C7=765
> > free_frozen:67988498 C0=516 C1=121 C2=85 C3=841 C4=67986468 C5=215 C6=76 C7=176
> > free_remove_partial:18 C4=18
> > free_slab:2831186 C4=2831186
> > free_slowpath:71825749 C0=609 C1=146 C2=104 C3=864 C4=71823538 C5=221 C6=84 C7=183
> > hwcache_align:0
> > min_partial:5
> > objects:2494
> > object_size:192
> > objects_partial:121
> > objs_per_slab:21
> > order:0
> > order_fallback:0
> > partial:14
> > poison:0
> > reclaim_account:0
> > red_zone:0
> > reserved:0
> > sanity_checks:0
> > slabs:127
> > slabs_cpu_partial:99(99) C1=25(25) C2=18(18) C3=23(23) C4=16(16) C5=4(4) C6=7(7) C7=6(6)
> > slab_size:192
> > store_user:0
> > total_objects:2667
> > trace:0
> > 
> 
> And the SLUB stats for the 2048 bytes slab is even worse : About every
> alloc/free is slow path
> 
> $ cd /sys/kernel/slab/:t-0002048 ; grep . *
> aliases:0
> align:8
> grep: alloc_calls: Function not implemented
> alloc_fastpath:8199220 C0=8196915 C1=306 C2=63 C3=297 C4=319 C5=550
> C6=722 C7=48
> alloc_from_partial:13931406 C0=13931401 C3=1 C5=4
> alloc_node_mismatch:0
> alloc_refill:70871657 C0=70871629 C1=2 C3=3 C4=9 C5=11 C6=3
> alloc_slab:1335 C0=1216 C1=17 C2=2 C3=15 C4=17 C5=22 C6=44 C7=2
> alloc_slowpath:155455299 C0=155455144 C1=18 C2=1 C3=21 C4=27 C5=40 C6=47
> C7=1

I certainly sympathize with your situation; these stats are even worse 
with netperf TCP_RR where slub regresses very heavily against slab.

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