Re: [dpdk-dev] [PATCH 04/29] net/ena/base: set default hash key

["Michał Krawczyk" <mk@semihalf.com>]

wt., 31 mar 2020 o 11:40 Michał Krawczyk <mk@semihalf.com> napisał(a):
>
> pt., 27 mar 2020 o 12:12 Andrew Rybchenko <arybchenko@solarflare.com>
> napisał(a):
> >
> > On 3/27/20 1:17 PM, Michal Krawczyk wrote:
> > > The RSS hash key was present in the device, but it wasn't exposed to
> > > the user. The other key still cannot be set, but now it can be accessed
> > > if one needs to do that.
> > >
> > > By default, the random hash key is used and it is generated only once
> > > when requested for the first time.
> > >
> > > Signed-off-by: Michal Krawczyk <mk@semihalf.com>
> > > Reviewed-by: Igor Chauskin <igorch@amazon.com>
> > > Reviewed-by: Guy Tzalik <gtzalik@amazon.com>
> >
> > [snip]
> >
> > > diff --git a/drivers/net/ena/ena_ethdev.c b/drivers/net/ena/ena_ethdev.c
> > > index cab38152a7..4c1e4899d0 100644
> > > --- a/drivers/net/ena/ena_ethdev.c
> > > +++ b/drivers/net/ena/ena_ethdev.c
> > > @@ -256,6 +256,22 @@ static const struct eth_dev_ops ena_dev_ops = {
> > >       .reta_query           = ena_rss_reta_query,
> > >  };
> > >
> > > +void ena_rss_key_fill(void *key, size_t size)
> > > +{
> > > +     static bool key_generated;
> > > +     static uint8_t default_key[ENA_HASH_KEY_SIZE];
> >
> > You have thread-safety patches in the series before this one.
> > Is it OK to be thread-unsafe here?
> >

I forgot to refer to this comment, sorry. ena_rss_key_fill() is called
only from ena_start() and as far as I know, it can be called only from
single-threaded context (device configuration flow). In that case,
there is no risk and we can be thread-unsafe.

> > > +
> > > +     RTE_ASSERT(size <= ENA_HASH_KEY_SIZE);
> > > +
> > > +     if (unlikely(!key_generated)) {
> >
> > I believe that unlikely() is not required here. It is not a
> > datapath and there is no point to use likely/unlikely on
> > control path.
> >
>
> I will remove it in v2.
>
> > > +             for (size_t i = 0; i < ENA_HASH_KEY_SIZE; ++i)
> >
> > It is C99 feature which breaks DPDK build pretty often, since
> > neither c99 nor higher are requested in default DPDK build.
> >
>
> Ok, will be fixed in v2.
>
> > > +                     default_key[i] = rte_rand() & 0xff;
> > > +             key_generated = true;
> > > +     }
> > > +
> > > +     rte_memcpy(key, default_key, size);
> > > +}
> > > +
> > >  static inline void ena_rx_mbuf_prepare(struct rte_mbuf *mbuf,
> > >                                      struct ena_com_rx_ctx *ena_rx_ctx)
> > >  {
> > >
> >