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Date: Wed, 3 Apr 2024 09:55:02 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>, Andrii Nakryiko
 <andrii@kernel.org>, linux-trace-kernel@vger.kernel.org,
 bpf@vger.kernel.org, jolsa@kernel.org, "Paul E . McKenney"
 <paulmck@kernel.org>, Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] ftrace: make extra rcu_is_watching() validation check
 optional
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On Tue, 2 Apr 2024 22:21:00 -0700
Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:

> > I just checked our fleet-wide production data for the last 24 hours.
> > Within the kprobe/kretprobe code path (ftrace_trampoline and
> > everything called from it), rcu_is_watching (both calls, see below)
> > cause 0.484% CPU cycles usage, which isn't nothing. So definitely we'd
> > prefer to be able to avoid that in production use cases.
> >  
> 
> I just ran synthetic microbenchmark testing multi-kretprobe
> throughput. We get (in millions of BPF kretprobe-multi program
> invocations per second):
>   - 5.568M/s as baseline;
>   - 5.679M/s with changes in this patch (+2% throughput improvement);
>   - 5.808M/s with disabling rcu_is_watching in rethook_try_get()
> (+2.3% more vs just one of rcu_is_watching, and +4.3% vs baseline).
> 
> It's definitely noticeable.

Ah, thanks for verifying (I should have read the thread before replying to
the previous email).

-- Steve