[PATCH 5/5] net: macb: Fix race between HW and driver
davem at davemloft.net
Mon May 5 13:56:53 PDT 2014
From: Soren Brinkmann <soren.brinkmann at xilinx.com>
Date: Sun, 4 May 2014 15:43:02 -0700
> Under "heavy" RX load, the driver cannot handle the descriptors fast
> enough. In detail, when a descriptor is consumed, its used flag is
> cleared and once the RX budget is consumed all descriptors with a
> cleared used flag are prepared to receive more data. Under load though,
> the HW may constantly receive more data and use those descriptors with a
> cleared used flag before they are actually prepared for next usage.
> The head and tail pointers into the RX-ring should always be valid and
> we can omit clearing and checking of the used flag.
> Signed-off-by: Soren Brinkmann <soren.brinkmann at xilinx.com>
Isn't the RX_USED bit the only thing that controls what RX entries
the chip will try to use?
I can't see how you can just remove the RX_USED bit handling
The problem actually seems to be that in the current code we clear the
RX_USED bit before we actually reallocate the buffer and set it up.
It should be a bug to see the RX_USED bit set in gem_rx_refill(), and
the only reason why it can happen is exactly because you're clearing it
too early in gem_rx().
This change doesn't seem to be correct, I'm not applying this series
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