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

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Date:   Sun, 13 Nov 2022 21:47:12 +0800
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>
To:     Leon Romanovsky <leon@...nel.org>
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

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@...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?
>
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
>>
> .