linux-kernel - Re: [PATCH] x86/alternatives: remove false sharing in poke_int3

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Message-ID: <Z-EGvjhkg6llyX24@gmail.com>
Date: Mon, 24 Mar 2025 08:16:14 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Masami Hiramatsu <mhiramat@...nel.org>, x86@...nel.org,
	bpf@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>,
	Greg Thelen <gthelen@...gle.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] x86/alternatives: remove false sharing in
 poke_int3_handler()


* Eric Dumazet <edumazet@...gle.com> wrote:

> > What's the adversarial workload here? Spamming bpf_stats_enabled on all
> > CPUs in parallel? Or mixing it with some other text_poke_bp_batch()
> > user if bpf_stats_enabled serializes access?
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> > Does anything undesirable happen in that case?
> 
> The case of multiple threads trying to flip bpf_stats_enabled is
> handled by bpf_stats_enabled_mutex.

So my suggested workload wasn't adversarial enough due to 
bpf_stats_enabled_mutex: how about some other workload that doesn't 
serialize access to text_poke_bp_batch()?

Thanks,

	Ingo