Re: [dpdk-dev] [PATCH v2 2/3] net/af_xdp: support pinning of IRQs

["Varghese, Vipin" <vipin.varghese@intel.com>]

Ok thanks

> -----Original Message-----
> From: Bruce Richardson <bruce.richardson@intel.com>
> Sent: Monday, October 21, 2019 7:26 PM
> To: Varghese, Vipin <vipin.varghese@intel.com>
> Cc: Loftus, Ciara <ciara.loftus@intel.com>; 'Stephen Hemminger'
> <stephen@networkplumber.org>; 'dev@dpdk.org' <dev@dpdk.org>; Ye,
> Xiaolong <xiaolong.ye@intel.com>; Laatz, Kevin <kevin.laatz@intel.com>;
> Yigit, Ferruh <ferruh.yigit@intel.com>
> Subject: Re: [dpdk-dev] [PATCH v2 2/3] net/af_xdp: support pinning of IRQs
> 
> On Mon, Oct 21, 2019 at 02:45:05PM +0100, Varghese, Vipin wrote:
> > Hi Bruce,
> >
> > snipped
> > > >  This ability to have the driver pin the interrupts for the
> > > > > user would be a big timesaver for developers too, who may be
> > > > > constantly re- running apps when testing.
> > > > Here my understanding, user can not or should not pass DPDK cores
> > > > for
> > > interrupt pinning. So should we ask the driver to fetch
> > > `rte_eal_configuration` and ensure the same?
> > > >
> > >
> > > Actually I disagree. I think the user should pass the cores for
> > > interrupt pinning,
> > I agree to this.
> >
> > > because unlike other PMDs it is perfectly valid to have the
> > > interrupts pinned to dedicated cores separate from those used by DPDK.
> > My point is the same, but not on DPDK DP or service cores.
> >
> > >
> > > Or taking another example, suppose the app takes 8 cores in the
> > > coremask, but only one of those cores is to be used for I/O, what
> > > cores should the driver pin the interrupts to?
> > It can be cores on machine (guest or host) which is not used by DPDK.
> >
> >  It probably should be the same core used for I/O, but the
> > > driver can't know which cores will be for that, or alternatively the
> > > user might want to use AF_XDP split across two cores, in which case
> > > any core on the system might be the intended one for interrupts.
> > I agree to the patch, only difference in dev->probe function, should not there
> be validation to ensure the IRQ core is not DPDK core or Service core as the
> Interface is owned by kernel and for non matched eBPF skb buff is used by
> kernel.
> >
> No. Since the 5.4 kernel, it's a usable configuration to run both the kernel and
> userspace portions of AF_XDP on the same core. In order to get best
> performance with a fixed number of cores, this setup - with interrupts pinned
> to the polling RX core - is now recommended. [For absolute best perf using any
> number of cores, a separate interrupt core may still work best, though]
> 
> /Bruce