Hi Keith, On 03/21/2016 06:38 PM, Wiles, Keith wrote: >> On Mar 21, 2016, at 11:10 AM, Olivier Matz <olivier.matz at 6wind.com> wrote: >> >> When using RSS, the number of rxqs has to be a power of two. >> This is a problem because there is no API is dpdk that makes >> the application aware of that. >> >> A good compromise is to allow the application to request a >> number of rxqs that is not a power of 2, but having inactive >> queues that will never receive packets. In this configuration, >> a warning will be issued to users to let them know that >> this is not an optimal configuration. > > Not sure I like this solution. I think an error should be returned with a log > message instead. What if the next driver needs power of three or must be odd > or even number. > > The bigger problem is the application is no longer portable for any given nic > configuration. > > We need a method for the application to query the system for these types of > information. But as we do not have that API we need to just error the request > off.
The initial problem is that the driver says "I support a maximum of X queues" and if the application configures a lower number, it gets an error. There is no API in DPDK to tell that only specific number of queues are supported. Adding an API is a solution, but in this case it's probably overkill. With this patch, the driver can present the proper number of queues to the application, knowing that the spreading of the packets won't be ideal (some queues won't receive packets), but it will work. A step further in this direction would be to configure more queues than asked in hardware to do a better spreading, almost similar to what is done with RETA tables in mlx5. But this is more complicated to do, especially if we want it for 16.04. Hope this is clearer with the explanation. Regards, Olivier
