linux-kernel - Re: [PATCH v8] PCI: hotplug: Add a generic RAS tracepoint for hotplug event

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Message-ID: <9b46a12b-90e2-c1ba-9394-5caa23a5cad7@linux.intel.com>
Date: Tue, 20 May 2025 15:52:56 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Lukas Wunner <lukas@...ner.de>
cc: Shuai Xue <xueshuai@...ux.alibaba.com>, rostedt@...dmis.org, 
    linux-pci@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, 
    linux-edac@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
    helgaas@...nel.org, bhelgaas@...gle.com, tony.luck@...el.com, bp@...en8.de, 
    mhiramat@...nel.org, mathieu.desnoyers@...icios.com, oleg@...hat.com, 
    naveen@...nel.org, davem@...emloft.net, anil.s.keshavamurthy@...el.com, 
    mark.rutland@....com, peterz@...radead.org, tianruidong@...ux.alibaba.com
Subject: Re: [PATCH v8] PCI: hotplug: Add a generic RAS tracepoint for hotplug
 event

On Tue, 20 May 2025, Lukas Wunner wrote:

> On Tue, May 20, 2025 at 12:44:38PM +0200, Lukas Wunner wrote:
> > Link speed changes and device plug/unplug events are orthogonal,
> > I don't think they should be mixed together in the same event.
> > 
> > A link speed event can be signaled simultaneously to a plug event
> > and then user space can decide in which type of event it's
> > interested in.
> > 
> > That also avoids the awkwardness of having N/A values for the
> > link speed on unplug.
> 
> After thinking about this some more:
> 
> A link speed event could contain a "reason" field
> which indicates why the link speed changed,
> e.g. "hotplug", "autonomous", "thermal", "retrain", etc.
> 
> In other words, instead of mixing the infomation for hotplug
> and link speed events together in one event, a separate link
> speed event could point to hotplug as one possible reason for
> the new speed.

It will be somewhat challenging to link LBMS into what caused it, 
especially in cases where there is more than one LBMS following a single 
Link Retraining.

Do you have opinion on should the event be only recorded from LBMS/LABS 
if the speed changed from the previous value? The speed should probably 
also be reported also for the first time (initial enumeration, hotplugging 
a new board).

-- 
 i.