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

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Message-ID: <f4e0675e-caad-4a1f-85b4-6b651d8565cd@paulmck-laptop>
Date: Tue, 9 Jul 2024 09:57:39 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Matthew Wilcox <willy@...radead.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
	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>
Subject: Re: [PATCH 00/10] perf/uprobe: Optimize uprobes

On Tue, Jul 09, 2024 at 05:30:38PM +0100, Matthew Wilcox wrote:
> On Tue, Jul 09, 2024 at 05:10:45PM +0100, Matthew Wilcox wrote:
> > > So I fundamentally do not believe in per-VMA locking. Specifically for
> > > this case that would be trading one hot line for another. I tried
> > > telling people that, but it doesn't seem to stick :/
> > 
> > SRCU also had its own performance problems, so we've got problems one
> > way or the other.  The per-VMA lock probably doesn't work quite the way
> > you think it does, but it absoutely can be a hot cacheline.
> > 
> > I did propose a store-free variant at LSFMM 2022 and again at 2023,
> > but was voted down.  https://lwn.net/Articles/932298/
> 
> Actually, the 2022 version has a bit more of the flavour of the
> argument: https://lwn.net/Articles/893906/

Thank you for the citations!

>From what I can see, part of the problem is that applications commonly
running on Linux have worked around many of these limitations one way or
another, which makes it harder to find a real-world use case for which
the store-free lookup gives substantial benefits.  Perhaps this uprobes
case will be helpful in that regard.  (Hey, I can dream, can't I?)

							Thanx, Paul