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 19C881E5B62; Fri, 2 May 2025 11:23:27 +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=1746185014; cv=none; b=osDXjMz7z3TvR5RrTV/Pr9VN+i+4UsqNkekmmHrcX8UD7kONHuXPO59sxibhAp05FwEE9AkRCpGa3Oz1MqB7oMnm9SIYUUKehsyyOi6aFqsZLNuzxKIfnatunEPPGzT8pxsbi4w9Opvd/JQGZEPx0lIN3hmjD7f9NK9FWnFEKno= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746185014; c=relaxed/simple; bh=PRPW/uDt3qcKT5KOPbhmERJnNbucXaeqN2L1IjyyPX4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=aUCWQpoSrcP0KEtS9ljATKEOt7WiXA5RQ2z+e0iHBPRJeKQCPi3tt0EeYalYNgp2ATSgIPh+L2QvHQlqOv9R+GpI/hsa+uZofrQvEZLA+bgRvMLfVVWYFA+fIWQ5+1a1mWqy87yKc5dwVNsHTfdkX6Kp7houkXPsPp4kxzVElJo= 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=lmV94JNE; arc=none smtp.client-ip=90.155.50.34 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="lmV94JNE" 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=PRPW/uDt3qcKT5KOPbhmERJnNbucXaeqN2L1IjyyPX4=; b=lmV94JNEzV4MsUJuxpPUrg3Bax VPmVO1/zySgMAd5F2IJnFvPiwZNPECAQ1noECVKMioFjFmA+n5SOAzV+kGbk/f9S1iWtVP9rLg6cZ hHF7SAR0m7IaJh5tCHy2qA/R/vkevPz7ZR3+xa+Zh5GSLdg0ezbI6iHsuifF9HE00+OjyODMdnQyb JkPl44vhH6EmamOKaWacZeeUgT5U6RxA5F79Ex/83F13pJOquOWPbK7ely8gHy1uVeRQNWbA0aBQP f+nYHty39Jk6K+NlHv/lPYoCn7B5BgUPqoEMb82IHPQShd8FJim54uJ17ucrfOJGKm432KMXzRw1R RwhYSB9w==; 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 4.98.2 #2 (Red Hat Linux)) id 1uAoTJ-0000000FKnO-0XWf; Fri, 02 May 2025 11:22:27 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 6C1A530057C; Fri, 2 May 2025 13:22:16 +0200 (CEST) Date: Fri, 2 May 2025 13:22:16 +0200 From: Peter Zijlstra To: Dave Hansen Cc: Steven Rostedt , Valentin Schneider , linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-perf-users@vger.kernel.org, kvm@vger.kernel.org, linux-arch@vger.kernel.org, linux-modules@vger.kernel.org, linux-trace-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, Juri Lelli , Marcelo Tosatti , Yair Podemsky , Josh Poimboeuf , Daniel Wagner , Petr Tesarik , Nicolas Saenz Julienne , Frederic Weisbecker , "Paul E. McKenney" , Dave Hansen , Sean Christopherson , Juergen Gross , Ajay Kaher , Alexey Makhalov , Broadcom internal kernel review list , Russell King , Catalin Marinas , Will Deacon , Huacai Chen , WANG Xuerui , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Pawan Gupta , Paolo Bonzini , Arnd Bergmann , Jason Baron , Ard Biesheuvel , Luis Chamberlain , Petr Pavlu , Sami Tolvanen , Daniel Gomez , Naveen N Rao , Anil S Keshavamurthy , "David S. Miller" , Masami Hiramatsu , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Kees Cook , Shuah Khan , Masahiro Yamada , Alice Ryhl , Miguel Ojeda , "Mike Rapoport (Microsoft)" , Rong Xu , Rafael Aquini , Song Liu , Andrii Nakryiko , Dan Carpenter , Brian Gerst , "Kirill A. Shutemov" , Benjamin Berg , Vishal Annapurve , Randy Dunlap , John Stultz , Tiezhu Yang Subject: Re: [PATCH v5 00/25] context_tracking,x86: Defer some IPIs until a user->kernel transition Message-ID: <20250502112216.GZ4198@noisy.programming.kicks-ass.net> References: <20250429113242.998312-1-vschneid@redhat.com> <20250430132047.01d48647@gandalf.local.home> <019f6713-cfbd-466b-8fb5-dcd982cf8644@intel.com> Precedence: bulk X-Mailing-List: linux-kselftest@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: <019f6713-cfbd-466b-8fb5-dcd982cf8644@intel.com> On Wed, Apr 30, 2025 at 11:07:35AM -0700, Dave Hansen wrote: > Both AMD and Intel have hardware to do it. ARM CPUs do it too, I think. > You can go buy the Intel hardware off the shelf today. To be fair, the Intel RAR thing is pretty horrific :-( Definitely sub-par compared to the AMD and ARM things. Furthermore, the paper states it is a uarch feature for SPR with no guarantee future uarchs will get it (and to be fair, I'd prefer it if they didn't). Furthermore, I suspect it will actually be slower than IPIs for anything with more than 64 logical CPUs due to reduced parallelism.