netdev - Re: [net-next 09/10] bnxt_en: add support for software dynamic interrupt moderation

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Date:   Fri, 5 Jan 2018 08:44:57 -0500
From:   Andy Gospodarek <andy@...yhouse.net>
To:     Michael Chan <michael.chan@...adcom.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        "michael.chan@...adcom.com" <mchan@...adcom.com>,
        talgi@...lanox.com, ogerlitz@...lanox.com,
        Andy Gospodarek <gospo@...adcom.com>
Subject: Re: [net-next 09/10] bnxt_en: add support for software dynamic
 interrupt moderation

On Thu, Jan 04, 2018 at 02:16:26PM -0800, Michael Chan wrote:
> On Thu, Jan 4, 2018 at 12:21 PM, Andy Gospodarek <andy@...yhouse.net> wrote:
> > From: Andy Gospodarek <gospo@...adcom.com>
> >
> > This implements the changes needed for the bnxt_en driver to add support
> > for dynamic interrupt moderation per ring.
> >
> > This does add additional counters in the receive path, but testing shows
> > that any additional instructions are offset by throughput gain when the
> > default configuration is for low latency.
> >
> > Signed-off-by: Andy Gospodarek <gospo@...adcom.com>
> > Cc: Michael Chan <mchan@...adcom.com>
> 
> Andy, looks good in general. I just have a few comments below.  These
> minor issues can be cleaned up after merge if you want.

Thanks for the review -- not the first time you've seen it :-) -- and for
agreeing that we can cleanup after the merge.  I'll need a v2, so I might as
well fix anything we want to fix now.

> 
> ....
> > +int bnxt_hwrm_set_ring_coal(struct bnxt *bp, struct bnxt_napi *bnapi)
> > +{
> > +       struct hwrm_ring_cmpl_ring_cfg_aggint_params_input req_rx = {0};
> > +       struct bnxt_cp_ring_info *cpr = &bnapi->cp_ring;
> > +       struct bnxt_coal coal;
> > +       unsigned int grp_idx;
> > +       int rc = 0;
> > +
> > +        /* Tick values in micro seconds.
> > +         * 1 coal_buf x bufs_per_record = 1 completion record.
> > +         */
> > +       memcpy(&coal, &bp->rx_coal, sizeof(struct bnxt_coal));
> > +
> > +       coal.coal_ticks = cpr->rx_ring_coal.coal_ticks;
> > +       coal.coal_bufs = cpr->rx_ring_coal.coal_bufs;
> > +
> > +       if (!bnapi->rx_ring)
> > +               return -ENODEV;
> > +
> > +       bnxt_hwrm_cmd_hdr_init(bp, &req_rx,
> > +                              HWRM_RING_CMPL_RING_CFG_AGGINT_PARAMS, -1, -1);
> > +
> > +       bnxt_hwrm_set_coal_params(&coal, &req_rx);
> > +
> > +       mutex_lock(&bp->hwrm_cmd_lock);
> > +       grp_idx = bnapi->index;
> > +
> > +       req_rx.ring_id = cpu_to_le16(bp->grp_info[grp_idx].cp_fw_ring_id);
> > +
> > +       rc = _hwrm_send_message(bp, &req_rx, sizeof(req_rx),
> > +                               HWRM_CMD_TIMEOUT);
> > +       mutex_unlock(&bp->hwrm_cmd_lock);
> 
> You can use the hwrm_send_message() variant that does not require you
> to take the mutex.  You only need this variant and take the mutex if
> you need to check the firmware reply.
> 

OK, good to know.  I'll consider whether or not it is important to check
the reply.  I think I'd want to know if it failed, but I'm not sure what
I'd do were that error condition encountered....

> > +       return rc;
> > +}
> > +
> >  int bnxt_hwrm_set_coal(struct bnxt *bp)
> >  {
> >         int i, rc = 0;
> > @@ -5705,7 +5753,11 @@ static void bnxt_enable_napi(struct bnxt *bp)
> >         int i;
> >
> >         for (i = 0; i < bp->cp_nr_rings; i++) {
> 
> We only need to enable this for every completion ring that has an RX
> ring.  In some cases, for example when XDP is enabled, there will be a
> set of completion rings with only TX rings.  So I think we can
> optimize this for completion rings with RX only.

Good call.

> > +               struct bnxt_cp_ring_info *cpr = &bp->bnapi[i]->cp_ring;
> >                 bp->bnapi[i]->in_reset = false;
> > +
> > +               INIT_WORK(&cpr->am.work, bnxt_dim_work);
> > +               cpr->am.mode = NET_DIM_CQ_PERIOD_MODE_START_FROM_EQE;
> >                 napi_enable(&bp->bnapi[i]->napi);
> >         }
> >  }