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

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Date:   Wed, 6 Jan 2021 07:50:50 +0200
From:   Leon Romanovsky <leonro@...dia.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
CC:     Saeed Mahameed <saeedm@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Jakub Kicinski <kuba@...nel.org>, <linux-pci@...r.kernel.org>,
        <linux-rdma@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH mlx5-next 0/4] Dynamically assign MSI-X vectors count

On Sun, Jan 03, 2021 at 10:24:36AM +0200, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
>
> Hi,
>
> The number of MSI-X vectors is PCI property visible through lspci, that
> field is read-only and configured by the device.
>
> The static assignment of an amount of MSI-X vectors doesn't allow utilize
> the newly created VF because it is not known to the device the future load
> and configuration where that VF will be used.
>
> The VFs are created on the hypervisor and forwarded to the VMs that have
> different properties (for example number of CPUs).
>
> To overcome the inefficiency in the spread of such MSI-X vectors, we
> allow the kernel to instruct the device with the needed number of such
> vectors, before VF is initialized and bounded to the driver.
>
> Before this series:
> [root@...ver ~]# lspci -vs 0000:08:00.2
> 08:00.2 Ethernet controller: Mellanox Technologies MT27800 Family [ConnectX-5 Virtual Function]
> ....
> 	Capabilities: [9c] MSI-X: Enable- Count=12 Masked-
>
> Configuration script:
> 1. Start fresh
> echo 0 > /sys/bus/pci/devices/0000\:08\:00.0/sriov_numvfs
> modprobe -q -r mlx5_ib mlx5_core
> 2. Ensure that driver doesn't run and it is safe to change MSI-X
> echo 0 > /sys/bus/pci/devices/0000\:08\:00.0/sriov_drivers_autoprobe
> 3. Load driver for the PF
> modprobe mlx5_core
> 4. Configure one of the VFs with new number
> echo 2 > /sys/bus/pci/devices/0000\:08\:00.0/sriov_numvfs
> echo 21 > /sys/bus/pci/devices/0000\:08\:00.2/vf_msix_vec
>
> After this series:
> [root@...ver ~]# lspci -vs 0000:08:00.2
> 08:00.2 Ethernet controller: Mellanox Technologies MT27800 Family [ConnectX-5 Virtual Function]
> ....
> 	Capabilities: [9c] MSI-X: Enable- Count=21 Masked-
>
>
> Thanks
>
> Leon Romanovsky (4):
>   PCI: Configure number of MSI-X vectors for SR-IOV VFs
>   net/mlx5: Add dynamic MSI-X capabilities bits
>   net/mlx5: Dynamically assign MSI-X vectors count
>   net/mlx5: Allow to the users to configure number of MSI-X vectors

Hi Bjorn,

I would like to route the PCI patch through mlx5-next tree which will
be taken to the netdev and rdma trees.

This is needed to avoid any possible merge conflicts between three
subsystems PCI, netdev and RDMA.

Is it acceptable by you?

Thanks