Re: [PATCH] ipc/msg.c: mitigate the lock contention with percpu counter

Andrew Morton
2022-09-02T16:12:31Z

On Fri, 2 Sep 2022 23:22:43 +0800 Jiebin Sun <jiebin.sun@intel.com> wrote:

> The msg_bytes and msg_hdrs atomic counters are frequently
> updated when IPC msg queue is in heavy use, causing heavy
> cache bounce and overhead. Change them to percpu_counters
> greatly improve the performance. Since there is one unique
> ipc namespace, additional memory cost is minimal. Reading
> of the count done in msgctl call, which is infrequent. So
> the need to sum up the counts in each CPU is infrequent.
>
> Apply the patch and test the pts/stress-ng-1.4.0
> -- system v message passing (160 threads).
>
> Score gain: 3.38x

So this test became 3x faster?

> CPU: ICX 8380 x 2 sockets
> Core number: 40 x 2 physical cores
> Benchmark: pts/stress-ng-1.4.0
> -- system v message passing (160 threads)
>
> ...
>
> @@ -138,6 +139,14 @@ percpu_counter_add(struct percpu_counter *fbc, s64 amount)
> preempt_enable();
> }
>
> +static inline void
> +percpu_counter_add_local(struct percpu_counter *fbc, s64 amount)
> +{
> + preempt_disable();
> + fbc->count += amount;
> + preempt_enable();
> +}

What's this and why is it added?

It would be best to propose this as a separate preparatory patch.
Fully changelogged and perhaps even with a code comment explaining why
and when it should be used.

Thanks.