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

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Message-ID: <4B13A321.8070909@gmail.com>
Date:	Mon, 30 Nov 2009 11:49:05 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Michael Chan <mchan@...adcom.com>
CC:	"leitao@...ux.vnet.ibm.com" <leitao@...ux.vnet.ibm.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] bnx2: avoid flushing statistics when doing a MTU change

Michael Chan a écrit :
> 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.

Yes, but if you dont call bnx2_get_stats() netdev->stats will contain
possibly very old values.

At least, calling it will give one no more than second error.

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