linux-kernel - Re: [PATCH v2] PCI: Reduce delay after FLR of Microsoft MANA devices

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Message-ID: <b23fb8f4-0da7-4403-8a2d-665d5675be9c@linux.microsoft.com>
Date: Fri, 30 May 2025 09:26:16 -0700
From: Graham Whyte <grwhyte@...ux.microsoft.com>
To: Lukas Wunner <lukas@...ner.de>
Cc: linux-pci@...r.kernel.org, shyamsaini@...ux.microsoft.com,
 code@...icks.com, Okaya@...nel.org, bhelgaas@...gle.com,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: Reduce delay after FLR of Microsoft MANA devices



On 5/29/2025 3:34 AM, Lukas Wunner wrote:
> On Wed, May 28, 2025 at 06:10:47PM +0000, grwhyte@...ux.microsoft.com wrote:
>> Add a device-specific reset for Microsoft MANA devices with the FLR
>> delay reduced from 100ms to 10ms. While this is not compliant with the pci
>> spec, these devices safely complete the FLR much quicker than 100ms and
>> this can be reduced to optimize certain scenarios
> 
> How often do you reset these devices that 90 msec makes a difference?
> What are these "certain scenarios"?
> 
VF removal and rescan is the main scenario for runtime repairs and driver updates.
Doing this on scale with 100ms adds up to significant time across multiple VFs.

> There are already "d3hot_delay" and "d3cold_delay" members in
> struct pci_dev.  I'm wondering if it would make sense to add
> another one, say, "flr_delay".  That would allow other devices
> to reduce or lengthen the delay without each of them having to
> duplicate pcie_flr().  The code duplication makes this difficult
> to maintain long-term.
> 
This is a good suggestion, we can make this more generic.

> Thanks,
> 
> Lukas