netdev - Re: [PATCH net-next 00/13] resource management using devlink reload

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Date:   Tue, 15 Nov 2022 08:12:52 +0100
From:   Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com, edumazet@...gle.com,
        intel-wired-lan@...ts.osuosl.org, jiri@...dia.com,
        anthony.l.nguyen@...el.com, alexandr.lobakin@...el.com,
        wojciech.drewek@...el.com, lukasz.czapnik@...el.com,
        shiraz.saleem@...el.com, jesse.brandeburg@...el.com,
        mustafa.ismail@...el.com, przemyslaw.kitszel@...el.com,
        piotr.raczynski@...el.com, jacob.e.keller@...el.com,
        david.m.ertman@...el.com, leszek.kaliszczuk@...el.com
Subject: Re: [PATCH net-next 00/13] resource management using devlink reload

On Mon, Nov 14, 2022 at 07:07:54PM +0200, Leon Romanovsky wrote:
> On Mon, Nov 14, 2022 at 09:31:11AM -0600, Samudrala, Sridhar wrote:
> > On 11/14/2022 7:23 AM, Leon Romanovsky wrote:
> > > On Mon, Nov 14, 2022 at 01:57:42PM +0100, Michal Swiatkowski wrote:
> > > > Currently the default value for number of PF vectors is number of CPUs.
> > > > Because of that there are cases when all vectors are used for PF
> > > > and user can't create more VFs. It is hard to set default number of
> > > > CPUs right for all different use cases. Instead allow user to choose
> > > > how many vectors should be used for various features. After implementing
> > > > subdevices this mechanism will be also used to set number of vectors
> > > > for subfunctions.
> > > > 
> > > > The idea is to set vectors for eth or VFs using devlink resource API.
> > > > New value of vectors will be used after devlink reinit. Example
> > > > commands:
> > > > $ sudo devlink resource set pci/0000:31:00.0 path msix/msix_eth size 16
> > > > $ sudo devlink dev reload pci/0000:31:00.0
> > > > After reload driver will work with 16 vectors used for eth instead of
> > > > num_cpus.
> > > By saying "vectors", are you referring to MSI-X vectors?
> > > If yes, you have specific interface for that.
> > > https://lore.kernel.org/linux-pci/20210314124256.70253-1-leon@kernel.org/
> > 
> > This patch series is exposing a resources API to split the device level MSI-X vectors
> > across the different functions supported by the device (PF, RDMA, SR-IOV VFs and
> > in future subfunctions). Today this is all hidden in a policy implemented within
> > the PF driver.
> 
> Maybe we are talking about different VFs, but if you refer to PCI VFs,
> the amount of MSI-X comes from PCI config space for that specific VF.
> 
> You shouldn't set any value through netdev as it will cause to
> difference in output between lspci (which doesn't require any driver)
> and your newly set number.

If I understand correctly, lspci shows the MSI-X number for individual
VF. Value set via devlink is the total number of MSI-X that can be used
when creating VFs. As Jake said I will fix the code to track both
values. Thanks for pointing the patch.

> 
> Also in RDMA case, it is not clear what will you achieve by this
> setting too.
>

We have limited number of MSI-X (1024) in the device. Because of that
the amount of MSI-X for each feature is set to the best values. Half for
ethernet, half for RDMA. This patchset allow user to change this values.
If he wants more MSI-X for ethernet, he can decrease MSI-X for RDMA.

> Thanks

Thanks for reviewing