linux-kernel - Re: [PATCH 00/10] perf/uprobe: Optimize uprobes

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Message-ID: <91d37ad3-137b-4feb-8154-4deaa4b11dc3@paulmck-laptop>
Date: Tue, 9 Jul 2024 07:11:23 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Masami Hiramatsu <mhiramat@...nel.org>, mingo@...nel.org,
	andrii@...nel.org, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, oleg@...hat.com, jolsa@...nel.org,
	clm@...a.com, bpf <bpf@...r.kernel.org>, willy@...radead.org
Subject: Re: [PATCH 00/10] perf/uprobe: Optimize uprobes

On Tue, Jul 09, 2024 at 11:01:53AM +0200, Peter Zijlstra wrote:
> On Mon, Jul 08, 2024 at 05:25:14PM -0700, Andrii Nakryiko wrote:
> 
> > Quick profiling for the 8-threaded benchmark shows that we spend >20%
> > in mmap_read_lock/mmap_read_unlock in find_active_uprobe. I think
> > that's what would prevent uprobes from scaling linearly. If you have
> > some good ideas on how to get rid of that, I think it would be
> > extremely beneficial. 
> 
> That's find_vma() and friends. I started RCU-ifying that a *long* time
> ago when I started the speculative page fault patches. I sorta lost
> track of that effort, Willy where are we with that?
> 
> Specifically, how feasible would it be to get a simple RCU based
> find_vma() version sorted these days?

Liam's and Willy's Maple Tree work, combined with Suren's per-VMA locking
combined with some of Vlastimil's slab work is pushing in that direction.
I believe that things are getting pretty close.

As with your work in 2010 and MIT guy's work in 2013, corner-case
correctness and corner-case performance regressions continue to provide
quite a bit of good clean fun.

							Thanx, Paul