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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id D75A3C61D97 for ; Wed, 22 Nov 2023 11:40:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=DqbYT03MTBpCyEuHQ45ibuhmV3Gw9xhfXyCUI/mm6Wo=; b=QFhWbvlGg0x7Ie L5tvfpEkTMwoi+vyaXBIhrQjL28SoX+xWBnTQJ0AXZPbugWzuaTZyOzmQqTeZ7kiBDwnWDLm064xI avvW7lVK3aJqBpE06h42UlNOCfrYxlby2i2gEc38wEdvYvI7UiWn4iLknzu5t7uBpBbC7OPSucI/F Oe6WHBiBlCKgtyOPrATm6B4fbj2vrEx930ex/J8ltS7AYkIl20qsP9PbNg4nQriAkqz8w3skrPeMj K/W8cgAKOFaPzDB6lq7FKRBaXNHaNlqSP24YisMaTEdpJFOuaiabmTUczbmaTvTIDYsRsSEuQNWhV AeuossjTdDwvfhXCc0sw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1r5lam-001ZaX-1X; Wed, 22 Nov 2023 11:40:28 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1r5lah-001ZYq-2o for linux-arm-kernel@lists.infradead.org; Wed, 22 Nov 2023 11:40:26 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A5D531595; Wed, 22 Nov 2023 03:41:05 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.43.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id ED7423F7A6; Wed, 22 Nov 2023 03:40:16 -0800 (PST) Date: Wed, 22 Nov 2023 11:40:09 +0000 From: Mark Rutland To: Will Deacon Cc: Huang Shijie , catalin.marinas@arm.com, suzuki.poulose@arm.com, broonie@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, anshuman.khandual@arm.com, robh@kernel.org, oliver.upton@linux.dev, maz@kernel.org, patches@amperecomputing.com Subject: Re: [PATCH 0/4] arm64: an optimization for AmpereOne Message-ID: References: <20231122092855.4440-1-shijie@os.amperecomputing.com> <20231122094857.GA2959@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20231122094857.GA2959@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231122_034023_961788_710D18C8 X-CRM114-Status: GOOD ( 13.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Nov 22, 2023 at 09:48:57AM +0000, Will Deacon wrote: > On Wed, Nov 22, 2023 at 05:28:51PM +0800, Huang Shijie wrote: > > 0) Background: > > We found that AmpereOne benefits from aggressive prefetches when > > using 4K page size. > > We tend to shy away from micro-architecture specific optimisations in > the arm64 kernel as they're pretty unmaintainable, hard to test properly, > generally lead to bloat and add additional obstacles to updating our > library routines. > > Admittedly, we have something for Thunder-X1 in copy_page() (disguised > as ARM64_HAS_NO_HW_PREFETCH) but, frankly, that machine needed all the > help it could get and given where it is today I suspect we could drop > that code without any material consequences. > > So I'd really prefer not to merge this; modern CPUs should do better at > copying data. It's copy_to_user(), not rocket science. I agree, and I'd also like to drop ARM64_HAS_NO_HW_PREFETCH. Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel