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=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, T_DKIMWL_WL_HIGH,URIBL_BLOCKED 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 61B4BC46460 for ; Tue, 4 Jun 2019 10:35:23 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3B3C4245E0 for ; Tue, 4 Jun 2019 10:35:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="MmhHS1yN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3B3C4245E0 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=iJemlxRCaqVuWIoPGyfqQ3bXNktx1QKClM5T0JSn65I=; b=MmhHS1yNy/3Jghb6Rpd2vvi/6 5b2SCHmYvvM2m+OEbKSJnG3BimAg+Qd2PPsompHXeOsUHtvnEodNQXcpbbfZhh+weQPt0dlzcgANN NYe0h1ghp9aEr2MEpbHxPB07EFA7X5G55zNIvjqLIH4gcNtPfw6Qoy4zqFsKYfA1BCDMPpxx3HTFH V4s/JNBf9DIKZocs09xyNeLqBCsDRIYgW42X5Z6wkMsr+Cvf2QOy0tcA6TPzAzYOzg83IMKyfVXAj I/UvObzkUPsJ255dyZj5sBdvdz7QyW19qOKXuuUFJUZj8blwjKiSzCJG3jV5oAqFzUNi71pdxhWvL 4DwF5s/ww==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hY6mo-0005WI-0P; Tue, 04 Jun 2019 10:35:22 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hY6mk-0005VX-VV for linux-arm-kernel@lists.infradead.org; Tue, 04 Jun 2019 10:35:20 +0000 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 6032980D; Tue, 4 Jun 2019 03:35:16 -0700 (PDT) Received: from [10.37.8.2] (unknown [10.37.8.2]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A3E1A3F246; Tue, 4 Jun 2019 03:35:13 -0700 (PDT) Subject: Re: [PATCH v5 3/3] arm64/fpsimd: Don't disable softirq when touching FPSIMD/SVE state To: Catalin Marinas References: <20190521172139.21277-1-julien.grall@arm.com> <20190521172139.21277-4-julien.grall@arm.com> <20190603162534.GF63283@arrakis.emea.arm.com> <20190603212104.mhz7vvj7afb2p3yr@mbp> From: Julien Grall Message-ID: <5c159919-d220-f8dc-d609-b1b1b2844d4b@arm.com> Date: Tue, 4 Jun 2019 11:35:11 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190603212104.mhz7vvj7afb2p3yr@mbp> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190604_033519_022242_9B0489E5 X-CRM114-Status: GOOD ( 16.13 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvmarm@lists.cs.columbia.edu, ard.biesheuvel@linaro.org, julien.thierry@arm.com, marc.zyngier@arm.com, suzuki.poulose@arm.com, will.deacon@arm.com, christoffer.dall@arm.com, linux-kernel@vger.kernel.org, james.morse@arm.com, Dave.Martin@arm.com, 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+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Catalin, On 6/3/19 10:21 PM, Catalin Marinas wrote: > On Mon, Jun 03, 2019 at 05:25:34PM +0100, Catalin Marinas wrote: >> On Tue, May 21, 2019 at 06:21:39PM +0100, Julien Grall wrote: >>> Since a softirq is supposed to check may_use_simd() anyway before >>> attempting to use FPSIMD/SVE, there is limited reason to keep softirq >>> disabled when touching the FPSIMD/SVE context. Instead, we can simply >>> disable preemption and mark the FPSIMD/SVE context as in use by setting >>> CPU's fpsimd_context_busy flag. >> [...] >>> +static void get_cpu_fpsimd_context(void) >>> +{ >>> + preempt_disable(); >>> + __get_cpu_fpsimd_context(); >>> +} >> >> Is there anything that prevents a softirq being invoked between >> preempt_disable() and __get_cpu_fpsimd_context()? > > Actually, it shouldn't matter as the softirq finishes using the fpsimd > before the thread is resumed. If the softirqs is handled in a thread (i.e ksoftirqd), then preempt_disable() will prevent them to run. For softirq running on return from interrupt context, they will finish before using fpsimd before the thread is resumed. Softirq running after __get_cpu_fpsimd_context() is called will not be able to use FPSIMD (may_use_simd() returns false). Cheers, -- Julien Grall _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel