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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 64851C433F5 for ; Thu, 14 Oct 2021 17:09:45 +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 06E6B61053 for ; Thu, 14 Oct 2021 17:09:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 06E6B61053 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=movementarian.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=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:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=DZhOvqeh2e3iOLAMOZGHUrzN4LD7ujq4oWRYk+ny2yg=; b=fgcESB7WrTUZfQFFFPnJ/mhJqu Ep9NJlNeYQpqjm8mA2awOda23+z2Gcn3FFUBy9Dz8B3VAGV/kgi3Roo+6Z3sWMKaE4xNNltvOgw/2 blXzZ0aC00ztZPbRkj4WZzLfYXcI/Jef/zrDYqRa0B4YTOSCRfY/lYkm5ag5pYBOcpLdtORnpQm2u wFh02xs39jKUdbpW9NZr2od3IFB7omTen9uvGIdT9PGRH1iU9gSGMYVMyNeHUaS12DLKcV2CuKmYR lb2PZYi5vQ7a+mANylARQsffifCwWRiSjlzKQfOUiLNa2DrVdziCKhabC4RWI6Wo72ux41RWS/U04 8emnhZpw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mb4Eb-003wsp-3E; Thu, 14 Oct 2021 17:09:37 +0000 Received: from ssh.movementarian.org ([139.162.205.133] helo=movementarian.org) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mb4EY-003wsR-9u for linux-nvme@lists.infradead.org; Thu, 14 Oct 2021 17:09:35 +0000 Received: from movement by movementarian.org with local (Exim 4.94) (envelope-from ) id 1mb4EU-003hGV-Fj; Thu, 14 Oct 2021 18:09:30 +0100 Date: Thu, 14 Oct 2021 18:09:30 +0100 From: John Levon To: Keith Busch Cc: linux-nvme@lists.infradead.org, hch@lst.de, sagi@grimberg.me Subject: Re: [PATCHv2 2/2] nvme-pci: remove cached shadow doorbell offsets Message-ID: References: <20211014164543.1821327-1-kbusch@kernel.org> <20211014164543.1821327-3-kbusch@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211014164543.1821327-3-kbusch@kernel.org> X-Url: http://www.movementarian.org/ X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211014_100934_368281_E8302806 X-CRM114-Status: GOOD ( 10.09 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Thu, Oct 14, 2021 at 09:45:43AM -0700, Keith Busch wrote: > And when this feature is in use, the specification requires all queue > updates use this mechanism, so don't don't treat the admin queue > differently. Hi Keith, I think you might have missed the other email from me? This would cause implementation difficulties for a controller, right? Currently we presume that the admin queue's shadow doorbells aren't valid, so always look at the BAR0 location. Given we need to support older Linux versions, we don't have any non-hacky way to handle this: we'd need something horrible that presumes those Linux versions - and any other driver implementations - always leave the admin queue shadows at zero, so if we see a non-zero value, it must be doing shadow doorbells. It's unclear to me what the advantage of fixing this is, given Linux has been out of spec for so long. regards john