linux-kernel - Re: [RFC PATCH V3 00/26] vfio/pci: Back guest interrupts from Interrupt Message Store (IMS)

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Message-ID: <48b8a6ae-6275-40ca-9db0-86b96cb002de@intel.com>
Date:   Wed, 8 Nov 2023 08:52:25 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     "Tian, Kevin" <kevin.tian@...el.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "yishaih@...dia.com" <yishaih@...dia.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "tom.zanussi@...ux.intel.com" <tom.zanussi@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: Re: [RFC PATCH V3 00/26] vfio/pci: Back guest interrupts from
 Interrupt Message Store (IMS)

Hi Alex,

On 11/7/2023 3:06 PM, Alex Williamson wrote:
> That also sort of illustrates the point though that this series is
> taking a pretty broad approach to slicing up vfio-pci-core's SET_IRQS
> ioctl code path, enabling support for IMS backed interrupts, but in
> effect complicating the whole thing without any actual consumer to
> justify the complication.  Meanwhile I think the goal is to reduce
> complication to a driver that doesn't exist yet.  So it currently seems
> like a poor trade-off.
> 
> This driver that doesn't exist yet could implement its own SET_IRQS
> ioctl that backs MSI-X with IMS as a starting point.  Presumably we
> expect multiple drivers to require this behavior, so common code makes
> sense, but the rest of us in the community can't really evaluate how
> much it makes sense to slice the common code without seeing that
> implementation and how it might leverage, if not directly use, the
> existing core code.

I understand. I'm hearing the same from you and Jason. I plan to
work on addressing your feedback but will only share it when it can be
accompanied by a draft of the IDXD VDCM driver. Please let me know
if you prefer a different approach.

Reinette