linux-kernel - Re: [RFC 0/4] pci/sriov: support VFs dynamic addition

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Date:   Fri, 11 Nov 2022 18:39:19 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     "Longpeng(Mike)" <longpeng2@...wei.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, jianjay.zhou@...wei.com,
        zhuangshengen@...wei.com, arei.gonglei@...wei.com,
        yechuan@...wei.com, huangzhichao@...wei.com, xiehong@...wei.com
Subject: Re: [RFC 0/4] pci/sriov: support VFs dynamic addition

On Fri, Nov 11, 2022 at 10:27:18PM +0800, Longpeng(Mike) wrote:
> From: Longpeng <longpeng2@...wei.com>
> 
> We can enable SRIOV and add VFs by /sys/bus/pci/devices/..../sriov_numvfs, but
> this operation needs to spend lots of time if there has a large amount of VFs.      
>                                                             
> For example, if the machine has 10 PFs and 250 VFs per-PF, enable all the VFs
> concurrently would cost about 200-250ms. However most of them are not need to be
> used at the moment, so we can enable SRIOV first but add VFs on demand.

It is unclear what took 200-250ms, is it physical VF creation or bind of
the driver to these VFs?

If the latter, you can try with sriov_drivers_autoprobe set to true. This is how
ennoblement of large SR-IOV systems is done.

Also PCI spec declares "VF enable" bit, which is applicable to all VFs
associated to that PF, see section "9.3.3.3.1 VF Enable".

Thanks

> 
> This series introduces two interfaces:
> 1. sriov_numvfs_no_scan: enable SRIOV without add the VFs.
> 2. sriov_scan_vf_id: add a specific VF.
> 
> Longpeng (4):
>   pci/sriov: extract sriov_numvfs common helper
>   pci/sriov: add vf_bitmap to mark the vf id allocation
>   pci/sriov: add sriov_numfs_no_scan interface
>   pci/sriov: add sriov_scan_vf_id interface
> 
>  drivers/pci/iov.c | 162 +++++++++++++++++++++++++++++++++++++++++-----
>  drivers/pci/pci.h |   1 +
>  2 files changed, 148 insertions(+), 15 deletions(-)
> 
> -- 
> 2.23.0
>