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Tue, 10 Nov 2020 09:53:53 +0000 MIME-Version: 1.0 Date: Tue, 10 Nov 2020 09:53:53 +0000 From: Marc Zyngier To: Greg Kroah-Hartman Subject: Re: [PATCH v2 5/6] arm64: Advertise CPUs capable of running 32-bit applications in sysfs In-Reply-To: References: <20201109213023.15092-1-will@kernel.org> <20201109213023.15092-6-will@kernel.org> User-Agent: Roundcube Webmail/1.4.9 Message-ID: X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: gregkh@linuxfoundation.org, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, peterz@infradead.org, morten.rasmussen@arm.com, qais.yousef@arm.com, surenb@google.com, qperret@google.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201110_045357_093719_FF908256 X-CRM114-Status: GOOD ( 14.12 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, kernel-team@android.com, Quentin Perret , Peter Zijlstra , Catalin Marinas , Qais Yousef , Suren Baghdasaryan , Will Deacon , Morten Rasmussen , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-11-10 09:36, Greg Kroah-Hartman wrote: [...] > While punting the logic out to userspace is simple for the kernel, and > of course my first option, I think this isn't going to work in the > long-run and the kernel will have to "know" what type of process it is > scheduling in order to correctly deal with this nightmare as userspace > can't do that well, if at all. For that to happen, we must first decide which part of the userspace ABI we are prepared to compromise on. The most obvious one would be to allow overriding the affinity on exec, but I'm pretty sure it has bad interactions with cgroups, on top of violating the existing ABI which mandates that the affinity is inherited across exec. There may be other options (always make at least one 32bit-capable CPU part of the process affinity?), but they all imply some form of userspace visible regressions. Pick your poison... :-/ M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel