From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 32579C43381 for ; Fri, 15 Mar 2019 10:22:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 05D78218A5 for ; Fri, 15 Mar 2019 10:22:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728852AbfCOKWr (ORCPT ); Fri, 15 Mar 2019 06:22:47 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:56804 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727428AbfCOKWr (ORCPT ); Fri, 15 Mar 2019 06:22:47 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CCEC9A78; Fri, 15 Mar 2019 03:22:46 -0700 (PDT) Received: from [10.1.196.50] (e108454-lin.cambridge.arm.com [10.1.196.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 73BCD3F71D; Fri, 15 Mar 2019 03:22:45 -0700 (PDT) Subject: Re: [RFC PATCH] arm64/fpsimd: Don't disable softirq when touching FPSIMD/SVE state To: Dave Martin Cc: Sebastian Andrzej Siewior , Ard Biesheuvel , linux-arm-kernel , linux-rt-users@vger.kernel.org, Catalin Marinas , Will Deacon , Linux Kernel Mailing List References: <20190208165513.8435-1-julien.grall@arm.com> <20190213143029.ad2kzg7vtuo3zpjk@linutronix.de> <20190213153630.GK3567@e103592.cambridge.arm.com> <20190213165227.7ekekkxazhbaqxoe@linutronix.de> <20190214103449.GN3567@e103592.cambridge.arm.com> <32ba7e1e-37ce-c904-15e4-9c908e873479@arm.com> <20190304172535.v5pf7yboii7ayxnb@linutronix.de> <20190315100634.GN3567@e103592.cambridge.arm.com> From: Julien Grall Message-ID: <715fed53-7c2d-f5fd-813b-211b204475d6@arm.com> Date: Fri, 15 Mar 2019 10:22:43 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190315100634.GN3567@e103592.cambridge.arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/03/2019 10:06, Dave Martin wrote: > On Thu, Mar 14, 2019 at 06:07:19PM +0000, Julien Grall wrote: >> Hi Sebastian, >> >> On 3/4/19 5:25 PM, Sebastian Andrzej Siewior wrote: > > [...] > >>> It would increase the softirq latency but the question is how bad would >>> it be. It would continue once the SIMD section is done. >> >> On Arm, the kernel may use either FPSIMD or SVE (if supported by the >> platform). While the FPSIMD context is fairly small (~4K), the SVE context >> can be up to ~64KB. > > It's not quite as bad as that. The FPSIMD state is ~0.5K, with the SVE > state size being up to ~8.5K (though for today's implementations ~2K may > be considered typical). Whoops, I forgot to divide by 8. Thank you for spotting it! Cheers, -- Julien Grall