From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 31455483BD8 for ; Thu, 17 Sep 2026 08:58:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789635509; cv=none; b=kx36R2H0NvGeVHizFm/oivnj6lk7GgUCg6iStL/g4ObIKe07knFjIUHYah01egbYau+FGFFU+U5OlwfUaOFCRwManp1Pv4npIRcvgi2CB+oVoURy8LSfnfpKHrCr7C9DqkdlvlxI6KeNZbpJpskVyoqShjMOk2g/002xXhgPTPM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789635509; c=relaxed/simple; bh=r9Hsb5A8A3GqqbHHPz4KIbZGPT/GmeguhasatfJFwg4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=edwoXD4ilSE2V8r151u1uIXM4pwQ56e12HB+p2fGiEws9pQSzs4ks+8DVQYxGlHS0M4bRQ308HegcunqnYHBDjraCpd5QH/2hCYLhs47wjVfBu04jD2WYIa/C3e8XF3g06l+C4kdyabrQMa9bvsoLpUX8+j5EQ6QSp2h77Qzn+k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=MmbfaGWa; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass 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="MmbfaGWa" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=QYwsrhlB4PAiHmssQJ9tn87vQAe1ulAb6t/S45PZfVk=; b=MmbfaGWagfWJACmxBolFLghWiX QNJ54mmRd22gZa3zsbksqROzwTYu3vZgZLpYlgF2RLtZmYzccIpydS5bW1dxtyM5BUystjURa3zNd GeWcEmrKA13Y1LZdak82SR9P5ZyjV6/T87JHoSBNiUpKXhUT21v3toaF5Wrml1VmaI7W4EWwWlhcC TR8XvPewspBnJEWBVNRJ127YGHPkYBcKTMvycTtE6NdXK+snQ1HdvBjk/FkGHhfHvKo5h58umYDPr fQvdfLUcDAfSZgsEJe4bFNJtVx0fm586mTfO+HBoz90cADRfWZuj/MkClqy2Xqj6P9cyPMStequvw H6AE4M1Q==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1x77wU-000000099Qv-3ePL; Thu, 17 Sep 2026 08:58:07 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id AADFF300583; Thu, 17 Sep 2026 10:58:05 +0200 (CEST) Date: Thu, 17 Sep 2026 10:58:05 +0200 From: Peter Zijlstra To: Suleiman Souhlal Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Darren Hart , Davidlohr Bueso , =?iso-8859-1?Q?Andr=E9?= Almeida , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , zhidao su , John Stultz , Qais Yousef , ssouhlal@freebsd.org Subject: Re: [RFC PATCH 00/12] FUTEX_PING: A stealable futex using Proxy Execution. Message-ID: <20260917085805.GD2009045@noisy.programming.kicks-ass.net> References: <20260917043339.2093426-1-suleiman@google.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260917043339.2093426-1-suleiman@google.com> On Thu, Sep 17, 2026 at 04:33:24AM +0000, Suleiman Souhlal wrote: > Hello, > > This patch series adds a new type of PI futexes, PI Next Generation, > or PING (name coined by Steven Rostedt) (but other name suggestions > are welcome!), that differs from classic PI futexes in that they can > be stolen from the top waiter, and use Proxy Execution instead of > rtmutexes internally. > > The reason to allow the futexes to be stolen is that with classic PI > futex's strict handoff to the top waiter, new contending lockers are > now forced to wait in queue, which means that any locking operation > now becomes a scheduling event. With stealing, a contending locker has > the chance of taking the lock without blocking. The longer wait time > of blocked tasks can be mitigated by forcing the lock to be handed > off to them in a way that can't be stolen, when they've been stolen > from too much, to ensure they don't get starved. > > The use of Proxy Execution lets us also get Priority Inheritance for > for fair tasks, which PI futexes don't really allow. https://patch.msgid.link/1490204338-1856-1-git-send-email-longman%40redhat.com Also, the goal is to eventually delete rt_mutex and have it be the normal mutex, in which case the existing FUTEX_*_PI things will automagically work. So I'm thinking all of this is way premature.