linux-kernel - Re: [PATCH 00/10] Add PCIe Bandwidth Controller

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Date:   Tue, 12 Sep 2023 10:45:12 -0700
From:   srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Krishna Chaitanya Chundru <quic_krichai@...cinc.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>, linux-pm@...r.kernel.org,
        linux-pci@...r.kernel.org, Bjorn Helgaas <helgaas@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Lukas Wunner <lukas@...ner.de>,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alex Deucher <alexdeucher@...il.com>
Subject: Re: [PATCH 00/10] Add PCIe Bandwidth Controller

On Tue, 2023-09-12 at 15:52 +0300, Ilpo Järvinen wrote:
> On Mon, 11 Sep 2023, srinivas pandruvada wrote:
> > On Mon, 2023-09-11 at 18:47 +0300, Ilpo Järvinen wrote:
> > 
> > 

[...]

> > But I don't suggest using such method. This causes confusion and
> > difficult to change. For example if we increase range of P-state
> > control, then there is no way to know what is the start point of T-
> > states.
> 
> Yes. I understand it would be confusing.
> 
> > It is best to create to separate cooling devices for BW and link
> > width.
> 
> Okay. If that's the case, then I see no reason to add the Link Width 
> cooling device now as it could do nothing besides reporting the
> current 
> link width.
> 
> The only question that then remains is how to take this into account
> in 
> the naming of the cooling devices, currently PCIe_Port_<pci_name()>
> is 
> used but perhaps it would be better to change that to 
> PCIe_Port_Link_Speed_... to allow PCI_Port_Link_Width_... to be added
> later beside it?
It is better in that way to add BW controller later.

Also adding separate cooling device will let thermal configuration,
choose different method at different thermal thresholds or all
together.

Thanks,
Srinivas

> 
> > Also there is a requirement that anything you add to thermal sysfs,
> > it
> > should have some purpose for thermal control. I hope Link width
> > control
> > is targeted to similar use case BW control.
> 
> Ability to control Link Width seems to be part of PCIe 6.0 L0p.
> AFAICT, 
> the reasons are to lower/control power consumption so it seems to be 
> within scope.
> 
>