[ovs-dev] [v12 16/16] netdev: Optimize netdev_send_prepare_batch.

[Ferriter, Cian]

Hi Ian,

Thanks for the review. My responses are inline.

> -----Original Message-----
> From: Stokes, Ian <ian.stokes at intel.com>
> Sent: Tuesday 15 June 2021 18:04
> To: Ferriter, Cian <cian.ferriter at intel.com>; ovs-dev at openvswitch.org; Van Haaren, Harry <harry.van.haaren at intel.com>
> Cc: i.maximets at ovn.org; Gaetan Rivet <gaetanr at nvidia.com>; Sriharsha Basavapatna <sriharsha.basavapatna at broadcom.com>
> Subject: RE: [ovs-dev] [v12 16/16] netdev: Optimize netdev_send_prepare_batch.
> 
> > From: Harry van Haaren <harry.van.haaren at intel.com>
> >
> > Optimize for the best case here where all packets will be compatible
> > with 'netdev_flags'.
> >
> > Signed-off-by: Harry van Haaren <harry.van.haaren at intel.com>
> > Co-authored-by: Cian Ferriter <cian.ferriter at intel.com>
> > Signed-off-by: Cian Ferriter <cian.ferriter at intel.com>
> 
> Thanks for the patch Cian/Harry, comments inline.
> 
> In general I have a concern of the impact on HWOL cases here and how much it would affect that. Have you data on this? Any
> thoughts from other HWOL folks here?

>From our POV, we are optimizing the normal and error free case. We are impacting the error case. When a packet is not compatible with netdev_flags that packet will be deleted from the batch and a " VLOG_WARN_RL()" will be called. This is quite costly as it is.

I'm curious to see what other HWOL folks think.

> > ---
> >  NEWS         |  2 ++
> >  lib/netdev.c | 31 ++++++++++++++++++++++---------
> >  2 files changed, 24 insertions(+), 9 deletions(-)
> >
> > diff --git a/NEWS b/NEWS
> > index a7ec34af1..8ad3c98db 100644
> > --- a/NEWS
> > +++ b/NEWS
> > @@ -18,6 +18,8 @@ Post-v2.15.0
> >         CPU supports it. This enhances performance by using the native vpopcount
> >         instructions, instead of the emulated version of vpopcount.
> >       * Optimize dp_netdev_output by enhancing compiler optimization potential.
> > +     * Optimize netdev sending by assuming the happy case, and using fallback
> > +       for if the netdev doesnt meet the required HWOL needs of a packet.
> This sounds a bit too low level for a NEWS item. Would suggest changing to single line Optimize netdev sending for best case scenario.
> 

Agreed, your single line sounds better. I've fixed this in the next version.

> BR
> Ian
> 
> >     - ovs-ctl:
> >       * New option '--no-record-hostname' to disable hostname configuration
> >         in ovsdb on startup.
> > diff --git a/lib/netdev.c b/lib/netdev.c
> > index 91e91955c..29a5f1aa9 100644
> > --- a/lib/netdev.c
> > +++ b/lib/netdev.c
> > @@ -837,20 +837,33 @@ static void
> >  netdev_send_prepare_batch(const struct netdev *netdev,
> >                            struct dp_packet_batch *batch)
> >  {
> > -    struct dp_packet *packet;
> > -    size_t i, size = dp_packet_batch_size(batch);
> > +    struct dp_packet *p;
> > +    uint32_t i, size = dp_packet_batch_size(batch);
> > +    char *err_msg = NULL;
> >
> > -    DP_PACKET_BATCH_REFILL_FOR_EACH (i, size, packet, batch) {
> > -        char *errormsg = NULL;
> > +    for (i = 0; i < size; i++) {
> > +        p = batch->packets[i];
> > +        int pkt_ok = netdev_send_prepare_packet(netdev->ol_flags, p, &err_msg);
> >
> > -        if (netdev_send_prepare_packet(netdev->ol_flags, packet, &errormsg)) {
> > -            dp_packet_batch_refill(batch, packet, i);
> > +        if (OVS_UNLIKELY(!pkt_ok)) {
> > +            goto refill_loop;
> > +        }
> > +    }
> > +
> > +    return;
> > +
> > +refill_loop:
> > +    /* Loop through packets from the start of the batch again. This is the
> > +     * exceptional case where packets aren't compatible with 'netdev_flags'. */
> > +    DP_PACKET_BATCH_REFILL_FOR_EACH (i, size, p, batch) {
> > +        if (netdev_send_prepare_packet(netdev->ol_flags, p, &err_msg)) {
> > +            dp_packet_batch_refill(batch, p, i);
> >          } else {
> > -            dp_packet_delete(packet);
> > +            dp_packet_delete(p);
> >              COVERAGE_INC(netdev_send_prepare_drops);
> >              VLOG_WARN_RL(&rl, "%s: Packet dropped: %s",
> > -                         netdev_get_name(netdev), errormsg);
> > -            free(errormsg);
> > +                         netdev_get_name(netdev), err_msg);
> > +            free(err_msg);
> >          }
> >      }
> >  }
> > --
> > 2.31.1
> >
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