linux-kernel - Re: [PATCH 8/8] uprobes: switch to RCU Tasks Trace flavor for better performance

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Message-ID: <20240801093505.GP33588@noisy.programming.kicks-ass.net>
Date: Thu, 1 Aug 2024 11:35:05 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Andrii Nakryiko <andrii@...nel.org>
Cc: linux-trace-kernel@...r.kernel.org, oleg@...hat.com,
	rostedt@...dmis.org, mhiramat@...nel.org, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, jolsa@...nel.org, paulmck@...nel.org
Subject: Re: [PATCH 8/8] uprobes: switch to RCU Tasks Trace flavor for better
 performance

On Wed, Jul 31, 2024 at 02:42:56PM -0700, Andrii Nakryiko wrote:
> This patch switches uprobes SRCU usage to RCU Tasks Trace flavor, which
> is optimized for more lightweight and quick readers (at the expense of
> slower writers, which for uprobes is a fine tradeof) and has better
> performance and scalability with number of CPUs.
> 
> Similarly to baseline vs SRCU, we've benchmarked SRCU-based
> implementation vs RCU Tasks Trace implementation.

Yes, this one can be the trace flavour, the other one for the retprobes
must be SRCU because it crosses over into userspace. But you've not yet
done that side.

Anyway, I think I can make the SRCU read_{,un}lock() smp_mb()
conditional, much like we have for percpu_rwsem and trace rcu, but I
definitely don't have time to poke at that in the foreseeable future :(