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From: Thomas Gleixner <tglx@linutronix.de>
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To: Zijiang Huang <huangzjsmile@gmail.com>, lukas@wunner.de
Cc: bhelgaas@google.com, flyingpeng@tencent.com, huangzjsmile@gmail.com,
 kerayhuang@tencent.com, linux-kernel@vger.kernel.org,
 linux-pci@vger.kernel.org
Subject: Re: [PATCH] PCI: Using lockless config space accessors based on
In-Reply-To: <20250507090407.2146324-1-kerayhuang@tencent.com>
References: <aBsRXO6Us_wsdhji@wunner.de>
 <20250507090407.2146324-1-kerayhuang@tencent.com>
Date: Wed, 07 May 2025 16:00:06 +0200
Message-ID: <877c2smsgp.ffs@tglx>
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On Wed, May 07 2025 at 17:04, Zijiang Huang wrote:
> I think it's safe to make this change for user-space accessors as well,
> since user-space only reads from proc files.

Again. See pci_cfg_access_lock()

>> Why is performance of the user space accessors important?
>> Perhaps because of vfio?
>
> During stability testing on large-scale machines (384+ CPUs), we always                                             > observed that heavy concurrent user-space access to PCI config space triggers 
> kernel softlockups.
>  
> Reproduction method: stress-ng --pci 384 

This is not really interesting as stress-ng is not a real world work
load.

What's the actual real world use case which uses those interfaces so
that the lock becomes an issue?

Thanks,

        tglx