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=-7.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 1CCFEC6377D for ; Thu, 22 Jul 2021 15:40:03 +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 DBFE86120C for ; Thu, 22 Jul 2021 15:40:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DBFE86120C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+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.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=iG8Wub4u7IP7nx25UFEYxLtUza/yf91dsetJxyk0zpA=; b=SqJyNPLQp+ubAa h0rjRdTG4yynwdOhHHfkthNr7WLeHJB/1XhsMQz6E/Rr1h/QrGj1XiwRwkDG/6q34ReCtyFbjbFsW u8V7e9hk2HS+PaYDM/ijJGGnNJXxxhO/7hJP43BrKbTC4qEu8QouSQHFonGB+YrXln3BNe94xyUOH P3pArGpDO5vC1kMRvCzVtNHcmKKApw/ZTjCr/XsyK1MZTPir6pl1xxfG95+vtredcniKH3S3gUc5T MEKr3La2y0HySLha6aa64apPN2GG8V1c5/6WEbyriEZFT1TcSdx7EYXG5uCGniJdTGdser5g3f5p7 Kgp5uFbZiQnL3Px5iOsg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1m6amH-0020B8-3y; Thu, 22 Jul 2021 15:38:25 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1m6amC-0020AO-Si for linux-arm-kernel@lists.infradead.org; Thu, 22 Jul 2021 15:38:22 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 52F186052B; Thu, 22 Jul 2021 15:38:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1626968299; bh=8nuwoZzIE9AXZnCM6wlUP00pAGYzYvAAKw+DrOsiFF4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GsDuiPbntO7mTbUHw/OMga6TpqxPzd1jVux3hSo8uaiVGT/FS1jJae4yyYqKXGFPa Tjh6LTF4MnLRwrMll7/BPTadvvds5880xaeoagTdakty199n46NPakMNOgptqU60cB P5gGX1qTC+Ri2ieYZ9XnV9h5HL+OIVKQciK2b4R4Mr/rNkCSUGXMt5qHwU6bIPeHqL OkhSNafLRHVCfxswugOTMybYqAbgOigkhZPr/eOPPP4Z9PWTsLf2BWWk17ESMh5rQS H+JD683PNUSwyaJGSrvqTMkk9WF3ym5GZXT3StPbQ9iWybwgJGZ5DxLDBOFkaC2VZb 5g3p3JN4p62sg== Date: Thu, 22 Jul 2021 16:38:15 +0100 From: Will Deacon To: Vladimir Murzin Cc: Shameerali Kolothum Thodi , "jean-philippe@linaro.org" , "maz@kernel.org" , "linux-kernel@vger.kernel.org" , Linuxarm , "catalin.marinas@arm.com" , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v2 3/3] kvm/arm: Align the VMID allocation with the arm64 ASID one Message-ID: <20210722153814.GA12566@willie-the-truck> References: <20210616155606.2806-1-shameerali.kolothum.thodi@huawei.com> <20210616155606.2806-4-shameerali.kolothum.thodi@huawei.com> <20210721163138.GD11003@willie-the-truck> <20210722095010.GA12012@willie-the-truck> <43b32e77-52b1-8524-63a1-c99578c2dd1d@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <43b32e77-52b1-8524-63a1-c99578c2dd1d@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210722_083820_990696_079BD320 X-CRM114-Status: GOOD ( 16.68 ) 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 Hi Vladimir, On Thu, Jul 22, 2021 at 04:22:26PM +0100, Vladimir Murzin wrote: > On 7/22/21 10:50 AM, Will Deacon wrote: > > As an aside: I'm more and more inclined to rip out the CnP stuff given > > that it doesn't appear to being any benefits, but does have some clear > > downsides. Perhaps something for next week. > > Can you please clarify what do you mean by "it doesn't appear to being any > benefits"? IIRC, Cortex-A65 implements CnP hint and I've heard that some > payloads seen improvement... Has anybody taped that out? I'd have thought building an SMT design in 2021 is a reasonably courageous thing to do. The issue I'm getting at is that modern cores seem to advertise CnP even if they ignore it internally, maybe because of some big/little worries? That would be fine if it didn't introduce complexity and overhead to the kernel, but it does and therefore I think we should rip it out (or at least stick it behind a "default n" config option if there are some niche users). There are also open questions as to exactly what CnP does because the architecture is not clear at all (for example TTBRx_EL1.CnP is permitted to be cached in a TLB). CHeers, Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel