Re: [net] 4890b686f4: netperf.Throughput_Mbps -69.4% regression
From: Feng Tang <hidden>
Date: 2022-06-28 03:49:41
Also in:
linux-mm, linux-s390, linux-sctp, lkml, mptcp, oe-lkp
On Mon, Jun 27, 2022 at 06:25:59PM +0200, Eric Dumazet wrote:
quoted hunk ↗ jump to hunk
On Mon, Jun 27, 2022 at 4:48 PM Feng Tang [off-list ref] wrote:quoted
Yes, I also analyzed the perf-profile data, and made some layout changes which could recover the changes from 69% to 40%. 7c80b038d23e1f4c 4890b686f4088c90432149bd6de 332b589c49656a45881bca4ecc0 ---------------- --------------------------- --------------------------- 15722 -69.5% 4792 -40.8% 9300 netperf.Throughput_MbpsI simply did the following and got much better results. But I am not sure if updates to ->usage are really needed that often...diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h index 679591301994d316062f92b275efa2459a8349c9..e267be4ba849760117d9fd041e22c2a44658ab36100644--- a/include/linux/page_counter.h +++ b/include/linux/page_counter.h@@ -3,12 +3,15 @@ #define _LINUX_PAGE_COUNTER_H #include <linux/atomic.h> +#include <linux/cache.h> #include <linux/kernel.h> #include <asm/page.h> struct page_counter { - atomic_long_t usage; - unsigned long min; + /* contended cache line. */ + atomic_long_t usage ____cacheline_aligned_in_smp; + + unsigned long min ____cacheline_aligned_in_smp; unsigned long low; unsigned long high; unsigned long max;@@ -27,12 +30,6 @@ struct page_counter { unsigned long watermark; unsigned long failcnt; - /* - * 'parent' is placed here to be far from 'usage' to reduce - * cache false sharing, as 'usage' is written mostly while - * parent is frequently read for cgroup's hierarchical - * counting nature. - */ struct page_counter *parent; };
I just tested it, it does perform better (the 4th is with your patch),
some perf-profile data is also listed.
7c80b038d23e1f4c 4890b686f4088c90432149bd6de 332b589c49656a45881bca4ecc0 e719635902654380b23ffce908d
---------------- --------------------------- --------------------------- ---------------------------
15722 -69.5% 4792 -40.8% 9300 -27.9% 11341 netperf.Throughput_Mbps
0.00 +0.3 0.26 ± 5% +0.5 0.51 +1.3 1.27 ± 2%pp.self.__sk_mem_raise_allocated
0.00 +0.3 0.32 ± 15% +1.7 1.74 ± 2% +0.4 0.40 ± 2% pp.self.propagate_protected_usage
0.00 +0.8 0.82 ± 7% +0.9 0.90 +0.8 0.84 pp.self.__mod_memcg_state
0.00 +1.2 1.24 ± 4% +1.0 1.01 +1.4 1.44 pp.self.try_charge_memcg
0.00 +2.1 2.06 +2.1 2.13 +2.1 2.11 pp.self.page_counter_uncharge
0.00 +2.1 2.14 ± 4% +2.7 2.71 +2.6 2.60 ± 2% pp.self.page_counter_try_charge
1.12 ± 4% +3.1 4.24 +1.1 2.22 +1.4 2.51 pp.self.native_queued_spin_lock_slowpath
0.28 ± 9% +3.8 4.06 ± 4% +0.2 0.48 +0.4 0.68 pp.self.sctp_eat_data
0.00 +8.2 8.23 +0.8 0.83 +1.3 1.26 pp.self.__sk_mem_reduce_allocated
And the size of 'mem_cgroup' is increased from 4224 Bytes to 4608.
Another info is the perf hotspos are slightly different between
tcp and sctp test cases.
Thanks,
Feng