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

[Longpeng (Mike, Cloud Infrastructure Service Product Dept.)]

Hi leon,

在 2022/11/12 0:39, Leon Romanovsky 写道:
> On Fri, Nov 11, 2022 at 10:27:18PM +0800, Longpeng(Mike) wrote:
> > From: Longpeng <longpeng2@xxxxxxxxxx>
> >
> > 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?
It is neither. In our test, we already created physical VFs before, so 
we skipped the 100ms waiting when writing PCI_SRIOV_CTRL. And our driver 
only probes PF, it just returns an error if the function is VF.

The hotspot is the sriov_add_vfs (but no driver probe in fact) which is 
a long procedure. Each step costs only a little, but the total cost is 
not acceptable in some time-sensitive cases.

What’s more, the sriov_add_vfs adds the VFs of a PF one by one. So we 
can mostly support 10 concurrent calls if there has 10 PFs.

> 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
> .