netdev - Re: [PATCH] bnx2: avoid flushing statistics when doing a MTU change

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Message-ID: <C27F8246C663564A84BB7AB34397724218065B9851@IRVEXCHCCR01.corp.ad.broadcom.com>
Date:	Mon, 30 Nov 2009 02:43:16 -0800
From:	"Michael Chan" <mchan@...adcom.com>
To:	"'Eric Dumazet'" <eric.dumazet@...il.com>,
	"leitao@...ux.vnet.ibm.com" <leitao@...ux.vnet.ibm.com>
cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] bnx2: avoid flushing statistics when doing a MTU
 change

Eric Dumazet wrote:

> leitao@...ux.vnet.ibm.com a écrit :
> > Actually when bnx2 changes the interface's MTU size, it resets
> > the chip and consequently flushes the interface statistics.
> > This patch saves the statistics in a temporary space in order to
> > maintain the statistics correct after the chip reset.
> >
> > Signed-off-by: Breno Leitao<leitao@...ux.vnet.ibm.com>
>
>
>
> >     return net_stats;
> >  }
> > @@ -6989,6 +7004,11 @@ bnx2_change_ring_size(struct bnx2
> *bp, u32 rx, u32 tx)
> >  {
> >     if (netif_running(bp->dev)) {
> >             bnx2_netif_stop(bp);
>
> I wonder if you need to renew this stats before copying them ?
>  (eg calling bnx2_get_stats())

Calling bnx2_get_stats() won't refresh the stats counters because
they are DMA'ed once a second.  There's an I/O to immediately DMA
the counters:

REG_WR(bp, BNX2_HC_COMMAND, bp->hc_cmd |
                                BNX2_HC_COMMAND_STATS_NOW);
REG_RD(bp, BNX2_HC_COMMAND);

We then need to add some delay to wait for the DMA to complete.

>
>
> > +
> > +           /* Save statistics that is going to be reseted */
> > +           memcpy(bp->stats_extra, &bp->dev->stats,
> > +                   sizeof(struct net_device_stats));
> > +
> >             bnx2_reset_chip(bp, BNX2_DRV_MSG_CODE_RESET);
> >             bnx2_free_skbs(bp);
> >             bnx2_free_mem(bp);

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