From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [RFC PATCH for 4.15 v12 00/22] Restartable sequences and CPU op vector Date: Wed, 22 Nov 2017 16:43:43 +0000 (UTC) Message-ID: <718035530.20074.1511369023901.JavaMail.zimbra@efficios.com> References: <20171121141900.18471-1-mathieu.desnoyers@efficios.com> <20171121172144.GL2482@two.firstfloor.org> <740195164.19702.1511301908907.JavaMail.zimbra@efficios.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andy Lutomirski Cc: Andi Kleen , Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , Dave Watson , linux-kernel , linux-api , Paul Turner , Andrew Morton , Russell King , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Hunter , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Will List-Id: linux-api@vger.kernel.org ----- On Nov 22, 2017, at 10:28 AM, Andy Lutomirski luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org wrote: > On Tue, Nov 21, 2017 at 2:05 PM, Mathieu Desnoyers > wrote: >> ----- On Nov 21, 2017, at 12:21 PM, Andi Kleen andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org wrote: >> >>> On Tue, Nov 21, 2017 at 09:18:38AM -0500, Mathieu Desnoyers wrote: >>>> Hi, >>>> >>>> Following changes based on a thorough coding style and patch changelog >>>> review from Thomas Gleixner and Peter Zijlstra, I'm respinning this >>>> series for another RFC. >>>> >>> My suggestion would be that you also split out the opv system call. >>> That seems to be main contention point currently, and the restartable >>> sequences should be useful without it. >> >> I consider rseq to be incomplete and a pain to use in various scenarios >> without cpu_opv. >> >> About the contention point you refer to: >> >> Using vDSO as an example of how things should be done is just wrong: the >> vDSO interaction with debugger instruction single-stepping is broken, >> as I detailed in my previous email. >> > > If anyone ever reports that as a problem, I'll gladly fix it in the > kernel. That's doable without an ABI change. If rseq-like things > started breaking single-stepping, we can't just fix it in the kernel. Very true. And rseq does break both line-level and instruction-level single-stepping. > > Also, there is one and only one vclock_gettime. Debuggers can easily > special-case it. For all I know, they already do. As my tests demonstrate, they don't. clock_gettime() vDSO currently breaks instruction-level single-stepping (istep) with gdb. I'll forward you the writeup I did on that a few days ago. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com