From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) (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 299D347FB0E for ; Tue, 15 Sep 2026 10:27:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=82.195.75.108 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789468046; cv=none; b=rsOaSAW7XkxgrFDH/lNE95xgLGrYiul58ZDjPExcSz7eyVsCxi8wGQLs+buBkTYIzZnL7Tj0cFXiY/rtYC2WiKGUCpj9ykIHQmXNaXhHDWIQ8zLbZpBIY7LLCKe3u9WmZfUc3gu/uDZg2RGNdGAglKwEyCkC9IofkfA7dnghYzs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789468046; c=relaxed/simple; bh=YSewos3xtxdk+prNKXaxelZ75btlblUdxtzeQBE8jXM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uDFEDDKp42DNOAAGhYGTsYMO1+sbrhFX8I6lGyhQk8eA36i1CPa5B+e3fQwyFQJlQmSWHdJQi9yJmwLlqFqtrApuo7Ci3w/wfSdmrINaKuap+p/iaOlgMP008lMIuMzoy+vioMT8MuCjop725THXqOpl8BgDHT/8bXqxZeV66iU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org; spf=pass smtp.mailfrom=debian.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b=GMdzIQ7c; arc=none smtp.client-ip=82.195.75.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=debian.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b="GMdzIQ7c" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=debian.org; s=smtpauto.stravinsky; h=X-Debian-User:In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=yqxuhklxm3wMqMiqJjzJAQ6bz6QwRVOq1Bpdvcb5rkk=; b=GMdzIQ7cB+pUr6XJoRX+kn4BpR QAa7Xq1deVr2ugxKOPxscTo4Wmd/PR/P2YT3jAlWuGg6a75wtQN8ZiSouRICsqiRSTtBSV5sWtnZ6 82ZmYTPfRXiglaSM2JhFU1VL0+QdKbEr5RZW9orpMY0hCOacKqkSiZ5ug2czJ3/mP04IGhwsIae6y IEviqdBDUQEy/DjyUQ0weYRTzqCaPeBXCcbepvIv7Hu7cdBB7IC7ZAi432ureBaDbEly5l0Pz8O8q iY2PlxNWjJkZPzeET2U1fvzM8VqKADKsvCnOADLjhmqpWQPJdAaEGBlRLjGuAK+q/7fguIChqZ5q6 0edPlNHg==; Received: from authenticated-user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.96) (envelope-from ) id 1x6QNg-004KHd-0x; Tue, 15 Sep 2026 10:27:16 +0000 Date: Tue, 15 Sep 2026 03:27:10 -0700 From: Breno Leitao To: Mark Rutland Cc: Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH] arm64/sve: Don't zero the SVE state buffer when the SVE state is live Message-ID: References: <20260914-b4-arm64-sve-acc-memset-v1-1-67866e442393@debian.org> Precedence: bulk X-Mailing-List: linux-kernel@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: X-Debian-User: leitao On Tue, Sep 15, 2026 at 11:15:01AM +0100, Mark Rutland wrote: > On Tue, Sep 15, 2026 at 02:50:27AM -0700, Breno Leitao wrote: > > On Tue, Sep 15, 2026 at 09:39:24AM +0100, Mark Rutland wrote: > > > > I've also dropped few other lines, but kept the benchmark values I've > > collected. Does this look better now? > > Yep, that looks good to me, with one minor nit below. > > With that fixed up, this all looks good. I assume you'll send a v2. > > > Author: Breno Leitao > > Date: Fri Sep 11 02:57:34 2026 -0700 > > > > arm64/sve: Don't zero the SVE state buffer when the SVE state is live > > > > Currently do_sve_acc() always zeroes current->thread.sve_state. This is > > not necessary in the common case, and avoiding the zeroing has a > > measurable impact on some benchmarks. > > > > In the common case where the task is not preempted and its state is not > > altered by a tracer, do_sve_acc() will observe that TIF_FOREIGN_FPSTATE > > is clear. In such cases, only the live register values matter, and the > > in-memory copy is stale regardless of whether it is saved in > > FP_STATE_FPSIMD format or FP_STATE_SVE format. > > > > This is worth doing because the SVE state is discarded on syscall entry, > ^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > That should say something like "It is worth skipping the zeroing > because". We deleted the line saying that skipping the zeroing was safe, > and so it's not clear what "this" is referring to. Ack, thanks for the feedback. I will send a v2 shortly. --breno