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McKenney" , Boqun Feng , Andy Lutomirski , 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 , Catalin Marinas , Will Deacon , Michael Kerrisk Subject: Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7) Message-ID: <20180416170240.mymd2kqfimydkhos@two.firstfloor.org> References: <20180412192800.15708-1-mathieu.desnoyers@efficios.com> <20180412192800.15708-13-mathieu.desnoyers@efficios.com> <20180412202302.xnw5jdl3upl46ywt@two.firstfloor.org> <751033048.11156.1523896094938.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <751033048.11156.1523896094938.JavaMail.zimbra@efficios.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: > Single-stepping is only a subset of the rseq limitations addressed > by cpu_opv. Anoher major limitation is algorithms requiring data > migration between per-cpu data structures safely against CPU hotplug, > and without having to change the cpu affinity mask. This is the case And how many people are going to implement such a complex separate path just for CPU hotplug? And even if they implement it how long before it bitrots? Seems more like a checkbox item than a realistic approach. > for memory allocators and userspace task schedulers which require > cpu_opv for migration between per-cpu memory pools and scheduler > runqueues. Not sure about that. Is that common? > > About the vgettimeofday and general handling of vDSO by gdb, gdb's > approach only takes care of line-by-line single-stepping by hiding > Linux' vdso mapping so users cannot target source code lines within > that shared object. However, it breaks instruction-level single-stepping. > I reported this issue to you back in Nov. 2017: > https://lkml.org/lkml/2017/11/20/803 It was known from day 1, but afaik never a problem. -Andi