netdev - Re: [PATCH v4 06/10] e1000e: Support for byte queue limits

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Message-ID: <CA+mtBx-8AzEyUc3GVD+mEQoqUZeaB9hjSJonRW_SjOQaTx51mQ@mail.gmail.com>
Date:	Wed, 30 Nov 2011 17:04:38 -0800
From:	Tom Herbert <therbert@...gle.com>
To:	Jesse Brandeburg <jesse.brandeburg@...el.com>
Cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v4 06/10] e1000e: Support for byte queue limits

> whats wrong with using total_tx_bytes or buffer_info->bytecount?  it
> contains the "bytes on the wire" value which will be slightly larger
> than skb->len, but avoids warming the skb->len cacheline unnecessarily.
>

This makes sense.  I made the changes, but the limits computed are
much higher than with using sbk->len.  I suspect there may be a bug in
GSO path.

For instance, in the driver at:

  bytecount = ((segs - 1) * skb_headlen(skb)) + skb->len;

I see cases like:

  segs=34, skb_header_len(skb)=70, skb->len=49298 so bytecount=51608

Which seems reasonable... but, I also see things like:

  segs=45, skb_header_len(skb)=1522, skb->len=65226, so bytecount= 132194
                                                      ^^^^
Which doesn't seem right at all.  I am thinking there may be a bug
setting skb->data_len improperly.

Tom
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