From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 43E652629D; Tue, 9 Jul 2024 15:31:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720539100; cv=none; b=pHic/34j5P39d+9DvpKLhBLhCJonrXwZw6evy6xGjQ+x6+zB8mOdJG+Rc61cdhDx3apY2l8keFh5aRXy53YSDb02R8vZLbhezHTM17IpVT7sa676gi15F8N8x2/cC4XmvJoCaa7hns02MeYTofI0WlivMC7Teqf++zAaa25dSBI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720539100; c=relaxed/simple; bh=2OvIRzYHPqXVR/b/m0jc1BGUjTadwusMYaHSMN75cuI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=P6cXdTdqZFN5z/RASA42b6ena4z3v8PEq4zpmvZ7aQcAcSS5I9rZSx++CKnYhHTB1EjjRShfaTIW12EGDkk2KrUANiIFD1gGFDXb1KXiPCRJ+1BvrUYFxfsiREmZRpo3J1iHNcURwOJQZ9pV5if207qqPis3zGiv1JmJS61bCW0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Oj4DWZPY; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Oj4DWZPY" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=E1R+7jPIXad3vJFym8KQnVYvqnqlBaz6UOE+8aD7j20=; b=Oj4DWZPYaR2AfqrV33ymLwuU0O S7WoDAk/hoJ+ju0IMofJIGqlBAViyUi+pZyjPYhbhgaXweRvIrrXOCH7FsbREwv1PCW2PPIadnmWB Lnrd/k/WgBOPLPJFB4lZiGSM7uVfhsLkOnzM95jkeo+l8e7Q9rln4JBnONhOV+48kvDjf9kol8yHy 0I6jLOTRGNE/ZicdKTJGoLmwfB7ja9pxbKmEMfQN+p8RL78G0uAmUrFPHJO4mRb0/8wAOUEoGBdDO W7EkRuljECkBypR0D6JumAM7xalr83IVc9BBNjHcI5mINZsK9jomjGqN+vojvp4j96hKjPvjppLfn 2/Hc3kEw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.97.1 #2 (Red Hat Linux)) id 1sRCoW-00000000leH-2LTK; Tue, 09 Jul 2024 15:31:33 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 2E3773006B7; Tue, 9 Jul 2024 17:31:32 +0200 (CEST) Date: Tue, 9 Jul 2024 17:31:32 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Andrii Nakryiko , Masami Hiramatsu , mingo@kernel.org, andrii@kernel.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, oleg@redhat.com, jolsa@kernel.org, clm@meta.com, bpf , willy@infradead.org Subject: Re: [PATCH 00/10] perf/uprobe: Optimize uprobes Message-ID: <20240709153132.GR27299@noisy.programming.kicks-ass.net> References: <20240708091241.544262971@infradead.org> <20240709075651.122204f1358f9f78d1e64b62@kernel.org> <20240709090153.GF27299@noisy.programming.kicks-ass.net> <91d37ad3-137b-4feb-8154-4deaa4b11dc3@paulmck-laptop> <20240709142943.GL27299@noisy.programming.kicks-ass.net> <445aed81-a845-4f5d-8b20-70eced3ce4f8@paulmck-laptop> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <445aed81-a845-4f5d-8b20-70eced3ce4f8@paulmck-laptop> On Tue, Jul 09, 2024 at 07:36:41AM -0700, Paul E. McKenney wrote: > > Per VMA refcounts or per VMA locks are a complete fail IMO. > > Not even to allow concurrent updates of the address space by different > threads of a process? Well, I'm sure it helps some workloads. But for others it is just moving the problem. > For me, per-VMA locking's need to RCU-protect the VMA is a good step > towards permitting RCU-protected scans of the Maple Tree, which then > gets lockless lookup. Right, the question is if the VMA lock is required to be stable against splitting. If that is the case, we're hosed :/ At the time I added a seqcount for that, but I'm also remembering that's one of the things people complained about for single threaded performance.