Re: [PATCH net-next v2 2/2] ptr_ring: make __ptr_ring_empty() checking more reliable

From: Michael S. Tsirkin
Date: Sun Jun 27 2021 - 02:09:58 EST

On Fri, Jun 25, 2021 at 05:20:10PM +0800, Yunsheng Lin wrote:
> On 2021/6/25 14:39, Michael S. Tsirkin wrote:
> > On Fri, Jun 25, 2021 at 11:18:56AM +0800, Yunsheng Lin wrote:
> >> 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：

How stable exactly? Try with -r so we can find out.

> ---------------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----------------------------------
>
> >
> >>
>