[Intel-wired-lan] [PATCH iwl-net] idpf: set completion tag for "empty" bufs associated with a packet

[Singh, Krishneil K]

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces at osuosl.org> On Behalf Of
> Simon Horman
> Sent: Thursday, October 17, 2024 2:04 AM
> To: Hay, Joshua A <joshua.a.hay at intel.com>
> Cc: intel-wired-lan at lists.osuosl.org; Lobakin, Aleksander
> <aleksander.lobakin at intel.com>; Chittim, Madhu
> <madhu.chittim at intel.com>; netdev at vger.kernel.org
> Subject: Re: [Intel-wired-lan] [PATCH iwl-net] idpf: set completion tag for
> "empty" bufs associated with a packet
> 
> On Mon, Oct 07, 2024 at 01:24:35PM -0700, Joshua Hay wrote:
> > Commit d9028db618a6 ("idpf: convert to libeth Tx buffer completion")
> > inadvertently removed code that was necessary for the tx buffer cleaning
> > routine to iterate over all buffers associated with a packet.
> >
> > When a frag is too large for a single data descriptor, it will be split
> > across multiple data descriptors. This means the frag will span multiple
> > buffers in the buffer ring in order to keep the descriptor and buffer
> > ring indexes aligned. The buffer entries in the ring are technically
> > empty and no cleaning actions need to be performed. These empty buffers
> > can precede other frags associated with the same packet. I.e. a single
> > packet on the buffer ring can look like:
> >
> > 	buf[0]=skb0.frag0
> > 	buf[1]=skb0.frag1
> > 	buf[2]=empty
> > 	buf[3]=skb0.frag2
> >
> > The cleaning routine iterates through these buffers based on a matching
> > completion tag. If the completion tag is not set for buf2, the loop will
> > end prematurely. Frag2 will be left uncleaned and next_to_clean will be
> > left pointing to the end of packet, which will break the cleaning logic
> > for subsequent cleans. This consequently leads to tx timeouts.
> >
> > Assign the empty bufs the same completion tag for the packet to ensure
> > the cleaning routine iterates over all of the buffers associated with
> > the packet.
> >
> > Fixes: d9028db618a6 ("idpf: convert to libeth Tx buffer completion")
> > Signed-off-by: Joshua Hay <joshua.a.hay at intel.com>
> > Acked-by: Alexander Lobakin <aleksander.lobakin at intel.com>
> > Reviewed-by: Madhu chittim <madhu.chittim at intel.com>
> 
> Thanks for the detailed description.
> 
> Reviewed-by: Simon Horman <horms at kernel.org>

Tested-by: Krishneil Singh <krishneil.k.singh at intel.com>