> >
> > On 2/24/2021 11:18 AM, Ciara Loftus wrote:
> > > This commit introduces support for preferred busy polling
> > > to the AF_XDP PMD. This feature aims to improve single-core
> > > performance for AF_XDP sockets under heavy load.
> > >
> > > A new vdev arg is introduced called 'busy_budget' whose default
> > > value is 64. busy_budget is the value supplied to the kernel
> > > with the SO_BUSY_POLL_BUDGET socket option and represents the
> > > busy-polling NAPI budget. To set the budget to a different value
> > > eg. 256:
> > >
> > > --vdev=net_af_xdp0,iface=eth0,busy_budget=256
> > >
> > > Preferred busy polling is enabled by default provided a kernel with
> > > version >= v5.11 is in use. To disable it, set the budget to zero.
> > >
> > > The following settings are also strongly recommended to be used in
> > > conjunction with this feature:
> > >
> > > echo 2 | sudo tee /sys/class/net/eth0/napi_defer_hard_irqs
> > > echo 200000 | sudo tee /sys/class/net/eth0/gro_flush_timeout
> > >
> > > .. where eth0 is the interface being used by the PMD.
> > >
> > > Signed-off-by: Ciara Loftus <ciara.lof...@intel.com>
> > > ---
> > > doc/guides/nics/af_xdp.rst | 38 ++++++++++++-
> > > drivers/net/af_xdp/compat.h | 13 +++++
> > > drivers/net/af_xdp/rte_eth_af_xdp.c | 85
> > ++++++++++++++++++++++++-----
> > > 3 files changed, 121 insertions(+), 15 deletions(-)
> >
> > Can you please update the release notes too to announce the feature?
>
> Will do.
>
> >
> > <...>
> >
> >
> > > @@ -39,3 +39,16 @@ create_shared_socket(struct xsk_socket **xsk_ptr
> > __rte_unused,
> > > return -1;
> > > }
> > > #endif
> > > +
> > > +#ifdef XDP_USE_NEED_WAKEUP
> > > +static int
> > > +syscall_needed(struct xsk_ring_prod *q, uint32_t busy_budget)
> > > +{
> > > + return xsk_ring_prod__needs_wakeup(q) | busy_budget;
> > > +}
> > > +#else
> > > +syscall_needed(struct xsk_ring_prod *q __rte_unused, uint32_t
> > busy_budget)
> > > +{
> > > + return busy_budget;
> > > +}
> >
> > Is the return type missing in the definition?
>
> Yes. Thanks for spotting this.
>
> >
> > Also for the case when both 'XDP_USE_NEED_WAKEUP' &
> > 'SO_PREFER_BUSY_POLL' this
> > function will always return '0', but current implementation doesn't know
> this
> > in
> > the compile time and compiler can't optimize for it, do you think does it
> make
> > sense to do this optimization?
>
> It makes sense assuming the compile environment and run environment are
> the same.
> However you make a valid point below. If the environments are different,
> we can't make this optimization because we can’t rely on the presence of the
> flags alone to tell us if these features are supported. More below.
>
> >
> > <...>
> >
> > > @@ -1628,8 +1670,22 @@ rte_pmd_af_xdp_probe(struct
> rte_vdev_device
> > *dev)
> > > return -EINVAL;
> > > }
> > >
> > > +#ifdef SO_PREFER_BUSY_POLL
> > > + busy_budget = busy_budget == -1 ?
> > ETH_AF_XDP_DFLT_BUSY_BUDGET :
> > > + busy_budget;
> > > + if (!busy_budget)
> > > + AF_XDP_LOG(ERR, "Preferred busy polling disabled\n");
> >
> > Is this an error case? What do you think changing the log level to DEBUG or
> > INFO?
>
> +1 for INFO
>
> >
> > Also how these compile time flags will work if the compiled environment
> and
> > run
> > environment kernel version are different and incompatible?
>
> This is a valid point. Right now if XDP_USE_NEED_WAKEUP is defined we
> assume the functionality is available in the kernel. If it's not, socket
> creation
> will fail and we abort. Perhaps we should retry socket creation without the
> flag if we get this failure. And record if support is available in a runtime
> variable. I'll look at adding this as another patch to the v2 series.
Hi Ferruh,
I looked at this a little more. For the v2 I'll make sure busy poll can work in
these environments with different compile-time and run-time kernels and use
setsockopt() to detect support in the kernel.
Since it will require significant changes and validation I'll submit a separate
series ensuring the same for the other existing flags (XDP_USE_NEED_WAKEUP /
XDP_UMEM_UNALIGNED_CHUNK_FLAG / shared umem).
Thanks,
Ciara
>
> >
> > Overall can it be possible to detect the support on runtime via
> 'setsockopt()'
> > without compile time macros and eliminate the compile time flags? Does it
> > make
> > sense?
>
> I think this can be done. It should allow applications compiled on older
> kernels without SO_PREFER_BUSY_POLL run on newer kernels with the
> feature.
> I will tackle this in the v2.
>
> Thanks for your feedback!
>
> Ciara
