netdev - Re: [PATCH net-next 05/18] gve: Add Gvnic stats AQ command and ethtool show/set-priv-flags.

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Message-ID: <20200825094635.715db5c0@kicinski-fedora-PC1C0HJN>
Date:   Tue, 25 Aug 2020 09:46:35 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Awogbemila <awogbemila@...gle.com>,
        Yangchun Fu <yangchun@...gle.com>
Cc:     netdev@...r.kernel.org, Kuo Zhao <kuozhao@...gle.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net-next 05/18] gve: Add Gvnic stats AQ command and
 ethtool show/set-priv-flags.

On Tue, 25 Aug 2020 08:46:12 -0700 David Awogbemila wrote:
> > > +     // stats from NIC
> > > +     RX_QUEUE_DROP_CNT               = 65,
> > > +     RX_NO_BUFFERS_POSTED            = 66,
> > > +     RX_DROPS_PACKET_OVER_MRU        = 67,
> > > +     RX_DROPS_INVALID_CHECKSUM       = 68,  
> >
> > Most of these look like a perfect match for members of struct
> > rtnl_link_stats64. Please use the standard stats to report the errors,
> > wherever possible.  
> These stats are based on the NIC stats format which don't exactly
> match rtnl_link_stats64.
> I'll add some clarification in the description and within the comments.

You must report standard stats. Don't be lazy and just dump everything
in ethtool -S and expect the user to figure out the meaning of your
strings.

> > > +static int gve_set_priv_flags(struct net_device *netdev, u32 flags)
> > > +{
> > > +     struct gve_priv *priv = netdev_priv(netdev);
> > > +     u64 ori_flags, new_flags;
> > > +     u32 i;
> > > +
> > > +     ori_flags = READ_ONCE(priv->ethtool_flags);
> > > +     new_flags = ori_flags;
> > > +
> > > +     for (i = 0; i < GVE_PRIV_FLAGS_STR_LEN; i++) {
> > > +             if (flags & BIT(i))
> > > +                     new_flags |= BIT(i);
> > > +             else
> > > +                     new_flags &= ~(BIT(i));
> > > +             priv->ethtool_flags = new_flags;
> > > +             /* set report-stats */
> > > +             if (strcmp(gve_gstrings_priv_flags[i], "report-stats") == 0) {
> > > +                     /* update the stats when user turns report-stats on */
> > > +                     if (flags & BIT(i))
> > > +                             gve_handle_report_stats(priv);
> > > +                     /* zero off gve stats when report-stats turned off */
> > > +                     if (!(flags & BIT(i)) && (ori_flags & BIT(i))) {
> > > +                             int tx_stats_num = GVE_TX_STATS_REPORT_NUM *
> > > +                                     priv->tx_cfg.num_queues;
> > > +                             int rx_stats_num = GVE_RX_STATS_REPORT_NUM *
> > > +                                     priv->rx_cfg.num_queues;
> > > +                             memset(priv->stats_report->stats, 0,
> > > +                                    (tx_stats_num + rx_stats_num) *
> > > +                                    sizeof(struct stats));  
> >
> > I don't quite get why you need the knob to disable some statistics.
> > Please remove or explain this in the cover letter. Looks unnecessary.  
> We use this to give the guest the option of disabling stats reporting
> through ethtool set-priv-flags. I'll update the cover letter.

I asked you why you reply a week later with "I want to give user the
option. I'll update the cover letter." :/ That's quite painful for the
reviewer. Please just provide the justification.

> > > @@ -880,6 +953,10 @@ static void gve_handle_status(struct gve_priv *priv, u32 status)
> > >               dev_info(&priv->pdev->dev, "Device requested reset.\n");
> > >               gve_set_do_reset(priv);
> > >       }
> > > +     if (GVE_DEVICE_STATUS_REPORT_STATS_MASK & status) {
> > > +             dev_info(&priv->pdev->dev, "Device report stats on.\n");  
> >
> > How often is this printed?  
> Stats reporting is disabled by default. But when enabled, this would
> only get printed whenever the virtual NIC detects
> an issue and triggers a report-stats request.

What kind of issue? Something serious? Packet drops?