Re: [dpdk-dev] [PATCH v3 1/1] bus/pci: optimise scanning with whitelist/blacklist

["Gaëtan Rivet" <grive@u256.net>]

On 20/04/20 12:25 +0530, Sunil Kumar Kori wrote:
> rte_bus_scan API scans all the available PCI devices irrespective of white
> or black listing parameters then further devices are probed based on white
> or black listing parameters. So unnecessary CPU cycles are wasted during
> rte_pci_scan.
> 
> For Octeontx2 platform with core frequency 2.4 Ghz, rte_bus_scan consumes
> around 26ms to scan around 90 PCI devices but all may not be used by the
> application. So for the application which uses 2 NICs, rte_bus_scan
> consumes few microseconds and rest time is saved with this patch.
> 

Hi Sunil,

The PCI bus was written at first with the understanding that all PCI
devices were scanned and made available on the bus -- the probe will filter
afterward.

Device hotplug and iteration were written with this in mind. Changing
this principle might have unintended consequences in other EAL parts.
I'm not fundamentally against it, but it is not how buses are currently
designed in DPDK.

To me, a one-time 26ms gain is not enough justification to change this
principle. How problematic is this for you? Do you encounter specific
issues due to this delay?

Thanks,
-- 
Gaëtan