linux-kernel - RE: [PATCH] PCI: hv: Only reuse existing IRTE allocation for Multi-MSI

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Message-ID: <SA1PR21MB1335FD78A02C0CE2632E532BBF6B9@SA1PR21MB1335.namprd21.prod.outlook.com>
Date:   Tue, 16 Aug 2022 21:13:26 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     "quic_jhugo@...cinc.com" <quic_jhugo@...cinc.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "robh@...nel.org" <robh@...nel.org>, "kw@...ux.com" <kw@...ux.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "boqun.feng@...il.com" <boqun.feng@...il.com>,
        Boqun Feng <Boqun.Feng@...rosoft.com>,
        Carl Vanderlip <quic_carlv@...cinc.com>
Subject: RE: [PATCH] PCI: hv: Only reuse existing IRTE allocation for
 Multi-MSI

> From: Bjorn Helgaas <helgaas@...nel.org>
> Sent: Tuesday, August 16, 2022 8:51 AM
> To: Dexuan Cui <decui@...rosoft.com>
> 
> 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.

> 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?

Thanks,
-- Dexuan