Re: [PATCH net-next v2 2/2] ptr_ring: make __ptr_ring_empty() checking more reliable
From: Yunsheng Lin <hidden>
Date: 2021-06-25 09:20:17
Also in:
linux-kselftest, lkml
On 2021/6/25 14:39, Michael S. Tsirkin wrote:
On Fri, Jun 25, 2021 at 11:18:56AM +0800, Yunsheng Lin wrote:quoted
Currently r->queue[] is cleared after r->consumer_head is moved forward, which makes the __ptr_ring_empty() checking called in page_pool_refill_alloc_cache() unreliable if the checking is done after the r->queue clearing and before the consumer_head moving forward. Move the r->queue[] clearing after consumer_head moving forward to make __ptr_ring_empty() checking more reliable. As a side effect of above change, a consumer_head checking is avoided for the likely case, and it has noticeable performance improvement when it is tested using the ptr_ring_test selftest added in the previous patch. Using "taskset -c 1 ./ptr_ring_test -s 1000 -m 0 -N 100000000" to test the case of single thread doing both the enqueuing and dequeuing: arch unpatched patched delta arm64 4648 ms 4464 ms +3.9% X86 2562 ms 2401 ms +6.2% Using "taskset -c 1-2 ./ptr_ring_test -s 1000 -m 1 -N 100000000" to test the case of one thread doing enqueuing and another thread doing dequeuing concurrently, also known as single-producer/single- consumer: arch unpatched patched delta arm64 3624 ms + 3624 ms 3462 ms + 3462 ms +4.4% x86 2758 ms + 2758 ms 2547 ms + 2547 ms +7.6%Nice but it's small - could be a fluke. How many tests did you run? What is the variance? Did you try pinning to different CPUs to observe numa effects? Please use perf or some other modern tool for this kind of benchmark. Thanks!
The result is quite stable, and retest using perf stat：
---------------unpatched ptr_ring.c begin----------------------------------
perf stat ./ptr_ring_test -s 1000 -m 0 -N 100000000
ptr_ring(size:1000) perf simple test for 100000000 times, took 2385198 us
Performance counter stats for './ptr_ring_test -s 1000 -m 0 -N 100000000':
2385.49 msec task-clock # 1.000 CPUs utilized
26 context-switches # 0.011 K/sec
0 cpu-migrations # 0.000 K/sec
57 page-faults # 0.024 K/sec
6202023521 cycles # 2.600 GHz
17424187640 instructions # 2.81 insn per cycle
<not supported> branches
6506477 branch-misses
2.385785170 seconds time elapsed
2.384014000 seconds user
0.000000000 seconds sys
root@(none):~# perf stat ./ptr_ring_test -s 1000 -m 0 -N 100000000
ptr_ring(size:1000) perf simple test for 100000000 times, took 2383385 us
Performance counter stats for './ptr_ring_test -s 1000 -m 0 -N 100000000':
2383.67 msec task-clock # 1.000 CPUs utilized
26 context-switches # 0.011 K/sec
0 cpu-migrations # 0.000 K/sec
57 page-faults # 0.024 K/sec
6197278066 cycles # 2.600 GHz
17424207772 instructions # 2.81 insn per cycle
<not supported> branches
6495766 branch-misses
2.383941170 seconds time elapsed
2.382215000 seconds user
0.000000000 seconds sys
root@(none):~# perf stat ./ptr_ring_test -s 1000 -m 0 -N 100000000
ptr_ring(size:1000) perf simple test for 100000000 times, took 2390858 us
Performance counter stats for './ptr_ring_test -s 1000 -m 0 -N 100000000':
2391.16 msec task-clock # 1.000 CPUs utilized
25 context-switches # 0.010 K/sec
0 cpu-migrations # 0.000 K/sec
57 page-faults # 0.024 K/sec
6216704120 cycles # 2.600 GHz
17424243041 instructions # 2.80 insn per cycle
<not supported> branches
6483886 branch-misses
2.391420440 seconds time elapsed
2.389647000 seconds user
0.000000000 seconds sys
root@(none):~# perf stat ./ptr_ring_test -s 1000 -m 0 -N 100000000
ptr_ring(size:1000) perf simple test for 100000000 times, took 2389810 us
Performance counter stats for './ptr_ring_test -s 1000 -m 0 -N 100000000':
2390.10 msec task-clock # 1.000 CPUs utilized
26 context-switches # 0.011 K/sec
0 cpu-migrations # 0.000 K/sec
58 page-faults # 0.024 K/sec
6213995715 cycles # 2.600 GHz
17424227499 instructions # 2.80 insn per cycle
<not supported> branches
6474069 branch-misses
2.390367070 seconds time elapsed
2.388644000 seconds user
0.000000000 seconds sys
---------------unpatched ptr_ring.c end----------------------------------
---------------patched ptr_ring.c begin----------------------------------
root@(none):~# perf stat ./ptr_ring_test_opt -s 1000 -m 0 -N 100000000
ptr_ring(size:1000) perf simple test for 100000000 times, took 2198894 us
Performance counter stats for './ptr_ring_test_opt -s 1000 -m 0 -N 100000000':
2199.18 msec task-clock # 1.000 CPUs utilized
23 context-switches # 0.010 K/sec
0 cpu-migrations # 0.000 K/sec
56 page-faults # 0.025 K/sec
5717671859 cycles # 2.600 GHz
16124164124 instructions # 2.82 insn per cycle
<not supported> branches
6564829 branch-misses
2.199445990 seconds time elapsed
2.197859000 seconds user
0.000000000 seconds sys
root@(none):~# perf stat ./ptr_ring_test_opt -s 1000 -m 0 -N 100000000
ptr_ring(size:1000) perf simple test for 100000000 times, took 2222337 us
Performance counter stats for './ptr_ring_test_opt -s 1000 -m 0 -N 100000000':
2222.63 msec task-clock # 1.000 CPUs utilized
23 context-switches # 0.010 K/sec
0 cpu-migrations # 0.000 K/sec
57 page-faults # 0.026 K/sec
5778632853 cycles # 2.600 GHz
16124210769 instructions # 2.79 insn per cycle
<not supported> branches
6603904 branch-misses
2.222901020 seconds time elapsed
2.221312000 seconds user
0.000000000 seconds sys
root@(none):~# perf stat ./ptr_ring_test_opt -s 1000 -m 0 -N 100000000
ptr_ring(size:1000) perf simple test for 100000000 times, took 2251980 us
Performance counter stats for './ptr_ring_test_opt -s 1000 -m 0 -N 100000000':
2252.28 msec task-clock # 1.000 CPUs utilized
25 context-switches # 0.011 K/sec
0 cpu-migrations # 0.000 K/sec
57 page-faults # 0.025 K/sec
5855668335 cycles # 2.600 GHz
16124310588 instructions # 2.75 insn per cycle
<not supported> branches
6777279 branch-misses
2.252543340 seconds time elapsed
2.250897000 seconds user
0.000000000 seconds sys
root@(none):~#
root@(none):~# perf stat ./ptr_ring_test_opt -s 1000 -m 0 -N 100000000
ptr_ring(size:1000) perf simple test for 100000000 times, took 2209415 us
Performance counter stats for './ptr_ring_test_opt -s 1000 -m 0 -N 100000000':
2209.70 msec task-clock # 1.000 CPUs utilized
24 context-switches # 0.011 K/sec
0 cpu-migrations # 0.000 K/sec
58 page-faults # 0.026 K/sec
5745003772 cycles # 2.600 GHz
16124198886 instructions # 2.81 insn per cycle
<not supported> branches
6508414 branch-misses
2.209973960 seconds time elapsed
2.208354000 seconds user
0.000000000 seconds sys
root@(none):~# perf stat ./ptr_ring_test_opt -s 1000 -m 0 -N 100000000
ptr_ring(size:1000) perf simple test for 100000000 times, took 2211409 us
Performance counter stats for './ptr_ring_test_opt -s 1000 -m 0 -N 100000000':
2211.70 msec task-clock # 1.000 CPUs utilized
24 context-switches # 0.011 K/sec
0 cpu-migrations # 0.000 K/sec
57 page-faults # 0.026 K/sec
5750136694 cycles # 2.600 GHz
16124176577 instructions # 2.80 insn per cycle
<not supported> branches
6553023 branch-misses
2.211968470 seconds time elapsed
2.210303000 seconds user
0.000000000 seconds sys
---------------patched ptr_ring.c end----------------------------------
quoted