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

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Date:   Tue, 12 Sep 2023 11:08:34 -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 10:45 -0700, srinivas pandruvada wrote:
> 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 
sorry, link width controller

> 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.
> > 
> > 
>