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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7EDFCC25B08 for ; Wed, 17 Aug 2022 07:51:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230190AbiHQHvl (ORCPT ); Wed, 17 Aug 2022 03:51:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229637AbiHQHvk (ORCPT ); Wed, 17 Aug 2022 03:51:40 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B99967A515; Wed, 17 Aug 2022 00:51:38 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 59B11CE1B94; Wed, 17 Aug 2022 07:51:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 22AF1C433D6; Wed, 17 Aug 2022 07:51:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1660722693; bh=iWwfXuklbTOD8tVpuV3XjT6Wa57Mj01ZLbe2IkbtdKc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=C2eph+kYna/HuHPyA/igO7h9P+7F2b0o8WDm4OrL0ynZwGSdrfx+cYjwJ5gJwounJ NNDhAJUY+DleGgqjH+/qi0OVe1DtS9o/uN9EIm2g8OvrEa/1I2W3nM5e0gcGyF4Uqs fKNIAzA7NLRzL8tXlkyTOEaP6kboP274qKMN+2Dim9FjzxSDwf+A89MikbaA+e71rM q2CoB/a1EuJaC4vyt0w1wu/EzTRkSrLddYbEy6WOyj6BSM+th77MDWdIercFxdNvz2 X25jolRrEVoDzivDpaqyx5KbRgv1diJ5/ERtnF2YNZJU+qgjNc5YegYlamnZHXbnMm nhgdJP5IK0/kg== Date: Wed, 17 Aug 2022 09:51:24 +0200 From: Lorenzo Pieralisi To: Dexuan Cui Cc: Bjorn Helgaas , "quic_jhugo@quicinc.com" , "wei.liu@kernel.org" , KY Srinivasan , Haiyang Zhang , Stephen Hemminger , "bhelgaas@google.com" , "linux-hyperv@vger.kernel.org" , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Michael Kelley (LINUX)" , "robh@kernel.org" , "kw@linux.com" , "alex.williamson@redhat.com" , "boqun.feng@gmail.com" , Boqun Feng , Carl Vanderlip Subject: Re: [PATCH] PCI: hv: Only reuse existing IRTE allocation for Multi-MSI Message-ID: References: <20220804025104.15673-1-decui@microsoft.com> <20220816155122.GA2064495@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Tue, Aug 16, 2022 at 09:13:26PM +0000, Dexuan Cui wrote: > > From: Bjorn Helgaas > > Sent: Tuesday, August 16, 2022 8:51 AM > > To: Dexuan Cui > > > > This has only observations with no explanations, and I don't see how > > it will be useful to future readers of the git history. > Please see the below. > > > I assume you bisected the problem to b4b77778ecc5? > Yes. > > > Can you just revert that? A revert requires no more explanation than > > "this broke something." > > It's better to not revert b4b77778ecc5, which is required by Jeff's > Multi-MSI device, which doesn't seem to be affected by the interrupt > issue I described. You must debug it, there are no two ways about it. We can't apply fixes on a hunch, more so given that I am not convinced at all this patch is fixing anything, it is just papering over an underlying bug that is still to be pinpointed. > > I guess this is a fine distinction, but I really don't like random > > code changes that "seem to avoid a problem but we don't know how." > > A revert at least has the advantage that we can cover our eyes and > > pretend the commit never happened. This patch feels like future > > readers will have to try to understand the code even though we > > clearly don't understand why it makes a difference. > > I just replied to Lorenzo's email with more details. FYI, this is the link > to my reply: > https://lwn.net/ml/linux-kernel/SA1PR21MB1335D08F987BBAE08EADF010BF6B9@SA1PR21MB1335.namprd21.prod.outlook.com/ > > I just felt the commit message might be too long if I had put all the > details there. :-) Can we add a Links: tag? Commit logs must describe the issue you are fixing, thouroughly and concisely. To start with "Jeffrey's 4 recent patches" is a very bad start for a commit log, it means nothing, try to read your log as someone who needs to understand the commit years down the line please. Now, back to this patch: we are at -rc1, unless Bjorn is willing to do so I am not inclined to apply this patch till next merge window (and actually I am not inclined to merge it at all). This gives you folks time to debug it (and it must be debugged), the fact that it works for one multi-MSI device does not mean that the bug isn't still there - I am worried that the issue is with b4b77778ecc5 and the interaction with core MSI/IOMMU. Thanks, Lorenzo