netdev - Re: [PATCH mlx5-next v7 0/4] Dynamically assign MSI-X vectors count

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Message-ID: <YEp01m0GiNzOSUV8@unreal>
Date:   Thu, 11 Mar 2021 21:51:50 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-rdma@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
        Don Dutile <ddutile@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "David S . Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH mlx5-next v7 0/4] Dynamically assign MSI-X vectors count

On Thu, Mar 11, 2021 at 11:37:28AM -0800, Alexander Duyck wrote:
> On Thu, Mar 11, 2021 at 10:17 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
> >
> > On Wed, Mar 10, 2021 at 03:34:01PM -0800, Alexander Duyck wrote:
> > > On Wed, Mar 10, 2021 at 11:09 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > > On Sun, Mar 07, 2021 at 10:55:24AM -0800, Alexander Duyck wrote:
> > > > > On Sun, Feb 28, 2021 at 11:55 PM Leon Romanovsky <leon@...nel.org> wrote:
> > > > > > From: Leon Romanovsky <leonro@...dia.com>
> > > > > >
> > > > > > @Alexander Duyck, please update me if I can add your ROB tag again
> > > > > > to the series, because you liked v6 more.
> > > > > >
> > > > > > Thanks
> > > > > >
> > > > > > ---------------------------------------------------------------------------------
> > > > > > Changelog
> > > > > > v7:
> > > > > >  * Rebase on top v5.12-rc1
> > > > > >  * More english fixes
> > > > > >  * Returned to static sysfs creation model as was implemented in v0/v1.

<...>

> > > representors rather than being actual PCIe devices. Having
> > > functionality that only works when the VF driver is not loaded just
> > > feels off. The VF sysfs directory feels like it is being used as a
> > > subdirectory of the PF rather than being a device on its own.
> >
> > Moving "virtfnX_msix_count" to the PF seems like it would mitigate
> > this somewhat.  I don't know how to make this work while a VF driver
> > is bound without making the VF feel even less like a PCIe device,
> > i.e., we won't be able to use the standard MSI-X model.
>
> Yeah, I actually do kind of like that idea. In addition it would
> address one of the things I pointed out as an issue before as you
> could place the virtfn values that the total value in the same folder
> so that it is all in one central spot rather than having to walk all
> over the sysfs hierarchy to check the setting for each VF when trying
> to figure out how the vectors are currently distributed.

User binds specific VF with specific PCI ID to VM, so instead of
changing MSI-X table for that specific VF, he will need to translate
from virtfn25_msix_count to PCI ID.

I also gave an example of my system where I have many PFs and VFs
function numbers are not distributed nicely. On that system virtfn25_msix_count
won't translate to AA:BB:CC.25 but to something else.

Thanks