netdev - Re: pktgen terminating condition

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Date:	Tue, 28 Aug 2007 15:56:19 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	msb@...gle.com
Cc:	netdev@...r.kernel.org, grundler@...gle.com, hadi@...erus.ca,
	robert.olsson@....uu.se, venza@...wnhat.org
Subject: Re: pktgen terminating condition

From: Mandeep Singh Baines <msb@...gle.com>
Date: Tue, 28 Aug 2007 15:47:18 -0700

> It seems that some drivers do not immediately free skbs on transmit
> complete.  They will hold the skb until there are more packets to
> free. One example is the sis900 driver which uses TX_IDLE (tx
> state-machine idle) instead of TX_OK (tx completed) as a way of
> coalescing interrupts. I've also seen another driver which does
> something similar. Not sure how prevalent this technique is.
>
> So is this a bug in the drivers or a bug in pktgen?

This is a bug since it can stall TCP sockets, and even non-TCP sockets
will not be freeable until these SKBs are released by the device.

All transmit packets must be released in a finite amount of time by
the driver without requiring more traffic to induce this release.
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