linux-kernel - Re: [PATCH v2 0/7] PCI: Replace short msleep() calls with more precise delay functions

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Message-ID: <c6efb55c-8ab9-4ccf-84c4-9a2a50102d15@163.com>
Date: Wed, 27 Aug 2025 01:07:23 +0800
From: Hans Zhang <18255117159@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: bhelgaas@...gle.com, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/7] PCI: Replace short msleep() calls with more
 precise delay functions



On 2025/8/23 00:46, Bjorn Helgaas wrote:
> On Fri, Aug 22, 2025 at 11:59:01PM +0800, Hans Zhang wrote:
>> This series replaces short msleep() calls (less than 20ms) with more
>> precise delay functions (fsleep() and usleep_range()) throughout the
>> PCI subsystem.
>>
>> The msleep() function with small values can sleep longer than intended
>> due to timer granularity, which can cause unnecessary delays in PCI
>> operations such as link status checking, reset handling, and hotplug
>> operations.
>>
>> These changes:
>> - Use fsleep() for delays that require precise timing (1-2ms).
>> - Use usleep_range() for delays that can benefit from a small range.
>> - Add #defines for all delay values with references to PCIe specifications.
>> - Update comments to reference the latest PCIe r7.0 specification.
>>
>> This improves the responsiveness of PCI operations while maintaining
>> compliance with PCIe specifications.
> 
> I would split this a little differently:
> 
>    - Add #defines for values from PCIe base spec.  Make the #define
>      value match the spec value.  If there's adjustment, e.g.,
>      doubling, do it at the sleep site.  Adjustment like this seems a
>      little paranoid since the spec should already have some margin
>      built into it.
> 
>    - Change to fsleep() (or usleep_range()) in separate patch.  There
>      might be discussion about these changes, but the #defines are
>      desirable regardless.
> 
> I'm personally dubious about the places you used usleep_range().
> These are low-frequency paths (rcar PHY ready, brcmstb link up,
> hotplug command completion, DPC recover) that don't seem critical.  I
> think they're all using made-up delays that don't come from any spec
> or hardware requirement anyway.  I think it's hard to make an argument
> for precision here.
> 

Dear Bjorn,

Thank you very much for your reply.

I have revised version v3 based on your review comments. Please continue 
your review. Thank you very much.

Best regards,
Hans

> Bjorn