2014-12-17 21:08 GMT+09:00 Jesper Dangaard Brouer <brouer@xxxxxxxxxx>:
> On Wed, 17 Dec 2014 16:13:49 +0900 Joonsoo Kim <js1304@xxxxxxxxx> wrote:
>
>> Ping... and I found another way to remove preempt_disable/enable
>> without complex changes.
>>
>> What we want to ensure is getting tid and kmem_cache_cpu
>> on the same cpu. We can achieve that goal with below condition loop.
>>
>> I ran Jesper's benchmark and saw 3~5% win in a fast-path loop over
>> kmem_cache_alloc+free in CONFIG_PREEMPT.
>>
>> 14.5 ns -> 13.8 ns
>
> Hi Kim,
>
> I've tested you patch. Full report below patch.
>
> Summary, I'm seeing 18.599 ns -> 17.523 ns (-1.076ns better).
Thanks for testing! :)
It will help to convince others.
Thanks.
> For network overload tests:
>
> Dropping packets in iptables raw, which is hitting the slub fast-path.
> Here I'm seeing an improvement of 3ns.
>
> For IP-forward, which is also invoking the slub slower path, I'm seeing
> an improvement of 6ns (I were not expecting to see any improvement
> here, the kmem_cache_alloc code is 24bytes smaller, so perhaps it's
> saving some icache).
>
> Full report below patch...
>
>> See following patch.
>>
>> Thanks.
>>
>> ----------->8-------------
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 95d2142..e537af5 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -2399,8 +2399,10 @@ redo:
>> * on a different processor between the determination of the pointer
>> * and the retrieval of the tid.
>> */
>> - preempt_disable();
>> - c = this_cpu_ptr(s->cpu_slab);
>> + do {
>> + tid = this_cpu_read(s->cpu_slab->tid);
>> + c = this_cpu_ptr(s->cpu_slab);
>> + } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid));
>>
>> /*
>> * The transaction ids are globally unique per cpu and per operation on
>> @@ -2408,8 +2410,6 @@ redo:
>> * occurs on the right processor and that there was no operation on the
>> * linked list in between.
>> */
>> - tid = c->tid;
>> - preempt_enable();
>>
>> object = c->freelist;
>> page = c->page;
>> @@ -2655,11 +2655,10 @@ redo:
>> * data is retrieved via this pointer. If we are on the same cpu
>> * during the cmpxchg then the free will succedd.
>> */
>> - preempt_disable();
>> - c = this_cpu_ptr(s->cpu_slab);
>> -
>> - tid = c->tid;
>> - preempt_enable();
>> + do {
>> + tid = this_cpu_read(s->cpu_slab->tid);
>> + c = this_cpu_ptr(s->cpu_slab);
>> + } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid));
>>
>> if (likely(page == c->page)) {
>> set_freepointer(s, object, c->freelist);
>
> SLUB evaluation 03
> ==================
>
> Testing patch from Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> slub fast-path
> preempt_{disable,enable} avoidance.
>
> Kernel
> ======
> Compiler: GCC 4.9.1
>
> Kernel config ::
>
> $ grep PREEMPT .config
> CONFIG_PREEMPT_RCU=y
> CONFIG_PREEMPT_NOTIFIERS=y
> # CONFIG_PREEMPT_NONE is not set
> # CONFIG_PREEMPT_VOLUNTARY is not set
> CONFIG_PREEMPT=y
> CONFIG_PREEMPT_COUNT=y
> # CONFIG_DEBUG_PREEMPT is not set
>
> $ egrep -e "SLUB|SLAB" .config
> # CONFIG_SLUB_DEBUG is not set
> # CONFIG_SLAB is not set
> CONFIG_SLUB=y
> # CONFIG_SLUB_CPU_PARTIAL is not set
> # CONFIG_SLUB_STATS is not set
>
> On top of::
>
> commit f96fe225677b3efb74346ebd56fafe3997b02afa
> Merge: 5543798 eea3e8f
> Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Date: Fri Dec 12 16:11:12 2014 -0800
>
> Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
>
>
> Setup
> =====
>
> netfilter_unload_modules.sh
> netfilter_unload_modules.sh
> sudo rmmod nf_reject_ipv4 nf_reject_ipv6
>
> base_device_setup.sh eth4 # 10G sink/receiving interface (ixgbe)
> base_device_setup.sh eth5
> sudo ethtool --coalesce eth4 rx-usecs 30
> sudo ip neigh add 192.168.21.66 dev eth5 lladdr 00:00:ba:d0:ba:d0
> sudo ip route add 198.18.0.0/15 via 192.168.21.66 dev eth5
>
>
> # sudo tuned-adm active
> Current active profile: latency-performance
>
> Drop in raw
> -----------
> alias iptables='sudo iptables'
> iptables -t raw -N simple || iptables -t raw -F simple
> iptables -t raw -I simple -d 198.18.0.0/15 -j DROP
> iptables -t raw -D PREROUTING -j simple
> iptables -t raw -I PREROUTING -j simple
>
> Generator
> ---------
> ./pktgen02_burst.sh -d 198.18.0.2 -i eth8 -m 90:E2:BA:0A:56:B4 -b 8 -t 3 -s 64
>
>
> Patch by Joonsoo Kim to avoid preempt in slub
> =============================================
>
> baseline: without patch
> -----------------------
>
> baseline kernel v3.18-7016-gf96fe22 at commit f96fe22567
>
> Type:kmem fastpath reuse Per elem: 46 cycles(tsc) 18.599 ns
> - (measurement period time:1.859917529 sec time_interval:1859917529)
> - (invoke count:100000000 tsc_interval:4649791431)
>
> alloc N-pattern before free with 256 elements
>
> Type:kmem alloc+free N-pattern Per elem: 100 cycles(tsc) 40.077 ns
> - (measurement period time:1.025993290 sec time_interval:1025993290)
> - (invoke count:25600000 tsc_interval:2564981743)
>
> single flow/CPU
> * IP-forward
> - instant rx:0 tx:1165376 pps n:60 average: rx:0 tx:1165928 pps
> (instant variation TX -0.407 ns (min:-0.828 max:0.507) RX 0.000 ns)
> * Drop in RAW (slab fast-path test)
> - instant rx:3245248 tx:0 pps n:60 average: rx:3245325 tx:0 pps
> (instant variation TX 0.000 ns (min:0.000 max:0.000) RX -0.007 ns)
>
> Christoph's slab_test, baseline kernel (at commit f96fe22567)::
>
> Single thread testing
> =====================
> 1. Kmalloc: Repeatedly allocate then free test
> 10000 times kmalloc(8) -> 49 cycles kfree -> 62 cycles
> 10000 times kmalloc(16) -> 48 cycles kfree -> 64 cycles
> 10000 times kmalloc(32) -> 53 cycles kfree -> 70 cycles
> 10000 times kmalloc(64) -> 64 cycles kfree -> 77 cycles
> 10000 times kmalloc(128) -> 74 cycles kfree -> 84 cycles
> 10000 times kmalloc(256) -> 84 cycles kfree -> 114 cycles
> 10000 times kmalloc(512) -> 83 cycles kfree -> 116 cycles
> 10000 times kmalloc(1024) -> 81 cycles kfree -> 120 cycles
> 10000 times kmalloc(2048) -> 104 cycles kfree -> 136 cycles
> 10000 times kmalloc(4096) -> 142 cycles kfree -> 165 cycles
> 10000 times kmalloc(8192) -> 238 cycles kfree -> 226 cycles
> 10000 times kmalloc(16384) -> 403 cycles kfree -> 264 cycles
> 2. Kmalloc: alloc/free test
> 10000 times kmalloc(8)/kfree -> 68 cycles
> 10000 times kmalloc(16)/kfree -> 68 cycles
> 10000 times kmalloc(32)/kfree -> 69 cycles
> 10000 times kmalloc(64)/kfree -> 68 cycles
> 10000 times kmalloc(128)/kfree -> 68 cycles
> 10000 times kmalloc(256)/kfree -> 68 cycles
> 10000 times kmalloc(512)/kfree -> 74 cycles
> 10000 times kmalloc(1024)/kfree -> 75 cycles
> 10000 times kmalloc(2048)/kfree -> 74 cycles
> 10000 times kmalloc(4096)/kfree -> 74 cycles
> 10000 times kmalloc(8192)/kfree -> 75 cycles
> 10000 times kmalloc(16384)/kfree -> 510 cycles
>
> $ nm --print-size vmlinux | egrep -e 'kmem_cache_alloc|kmem_cache_free|is_pointer_to_page'
> ffffffff81163bd0 00000000000000e1 T kmem_cache_alloc
> ffffffff81163ac0 000000000000010c T kmem_cache_alloc_node
> ffffffff81162cb0 000000000000013b T kmem_cache_free
>
>
> with patch
> ----------
>
> single flow/CPU
> * IP-forward
> - instant rx:0 tx:1174652 pps n:60 average: rx:0 tx:1174222 pps
> (instant variation TX 0.311 ns (min:-0.230 max:1.018) RX 0.000 ns)
> * compare against baseline:
> - 1174222-1165928 = +8294pps
> - (1/1174222*10^9)-(1/1165928*10^9) = -6.058ns
>
> * Drop in RAW (slab fast-path test)
> - instant rx:3277440 tx:0 pps n:74 average: rx:3277737 tx:0 pps
> (instant variation TX 0.000 ns (min:0.000 max:0.000) RX -0.028 ns)
> * compare against baseline:
> - 3277737-3245325 = +32412 pps
> - (1/3277737*10^9)-(1/3245325*10^9) = -3.047ns
>
> SLUB fast-path test: time_bench_kmem_cache1
> * modprobe time_bench_kmem_cache1 ; rmmod time_bench_kmem_cache1; sudo dmesg -c
>
> Type:kmem fastpath reuse Per elem: 43 cycles(tsc) 17.523 ns (step:0)
> - (measurement period time:1.752338378 sec time_interval:1752338378)
> - (invoke count:100000000 tsc_interval:4380843588)
> * difference: 17.523 - 18.599 = -1.076ns
>
> alloc N-pattern before free with 256 elements
>
> Type:kmem alloc+free N-pattern Per elem: 100 cycles(tsc) 40.369 ns (step:0)
> - (measurement period time:1.033447112 sec time_interval:1033447112)
> - (invoke count:25600000 tsc_interval:2583616203)
> * difference: 40.369 - 40.077 = +0.292ns
>
>
> Christoph's slab_test::
>
> Single thread testing
> =====================
> 1. Kmalloc: Repeatedly allocate then free test
> 10000 times kmalloc(8) -> 46 cycles kfree -> 61 cycles
> 10000 times kmalloc(16) -> 46 cycles kfree -> 63 cycles
> 10000 times kmalloc(32) -> 49 cycles kfree -> 69 cycles
> 10000 times kmalloc(64) -> 57 cycles kfree -> 76 cycles
> 10000 times kmalloc(128) -> 66 cycles kfree -> 83 cycles
> 10000 times kmalloc(256) -> 84 cycles kfree -> 110 cycles
> 10000 times kmalloc(512) -> 77 cycles kfree -> 114 cycles
> 10000 times kmalloc(1024) -> 80 cycles kfree -> 116 cycles
> 10000 times kmalloc(2048) -> 102 cycles kfree -> 131 cycles
> 10000 times kmalloc(4096) -> 135 cycles kfree -> 163 cycles
> 10000 times kmalloc(8192) -> 238 cycles kfree -> 218 cycles
> 10000 times kmalloc(16384) -> 399 cycles kfree -> 262 cycles
> 2. Kmalloc: alloc/free test
> 10000 times kmalloc(8)/kfree -> 65 cycles
> 10000 times kmalloc(16)/kfree -> 66 cycles
> 10000 times kmalloc(32)/kfree -> 65 cycles
> 10000 times kmalloc(64)/kfree -> 66 cycles
> 10000 times kmalloc(128)/kfree -> 66 cycles
> 10000 times kmalloc(256)/kfree -> 71 cycles
> 10000 times kmalloc(512)/kfree -> 72 cycles
> 10000 times kmalloc(1024)/kfree -> 71 cycles
> 10000 times kmalloc(2048)/kfree -> 71 cycles
> 10000 times kmalloc(4096)/kfree -> 71 cycles
> 10000 times kmalloc(8192)/kfree -> 65 cycles
> 10000 times kmalloc(16384)/kfree -> 511 cycles
>
> $ nm --print-size vmlinux | egrep -e 'kmem_cache_alloc|kmem_cache_free|is_pointer_to_page'
> ffffffff81163ba0 00000000000000c9 T kmem_cache_alloc
> ffffffff81163aa0 00000000000000f8 T kmem_cache_alloc_node
> ffffffff81162cb0 0000000000000133 T kmem_cache_free
>
>
>
> Kernel size change
> ------------------
>
> $ scripts/bloat-o-meter vmlinux vmlinux-kim-preempt-avoid
> add/remove: 0/0 grow/shrink: 0/8 up/down: 0/-248 (-248)
> function old new delta
> kmem_cache_free 315 307 -8
> kmem_cache_alloc_node 268 248 -20
> kmem_cache_alloc 225 201 -24
> kfree 274 250 -24
> __kmalloc_node_track_caller 356 324 -32
> __kmalloc_node 340 308 -32
> __kmalloc 324 273 -51
> __kmalloc_track_caller 343 286 -57
>
>
> Qmempool notes:
> ---------------
>
> On baseline kernel:
>
> Type:qmempool fastpath reuse SOFTIRQ Per elem: 33 cycles(tsc) 13.287 ns
> - (measurement period time:0.398628965 sec time_interval:398628965)
> - (invoke count:30000000 tsc_interval:996571541)
>
> Type:qmempool fastpath reuse BH-disable Per elem: 47 cycles(tsc) 19.180 ns
> - (measurement period time:0.575425927 sec time_interval:575425927)
> - (invoke count:30000000 tsc_interval:1438563781)
>
> qmempool_bench: N-pattern with 256 elements
>
> Type:qmempool alloc+free N-pattern Per elem: 62 cycles(tsc) 24.955 ns (step:0)
> - (measurement period time:0.638871008 sec time_interval:638871008)
> - (invoke count:25600000 tsc_interval:1597176303)
>
>
> --
> Best regards,
> Jesper Dangaard Brouer
> MSc.CS, Sr. Network Kernel Developer at Red Hat
> Author of http://www.iptv-analyzer.org
> LinkedIn: http://www.linkedin.com/in/brouer
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