RE: [Intel-wired-lan] [PATCH intel-net] i40e: fix receiving of single packets in xsk zero-copy mode

-----Original Message-----
From: Intel-wired-lan <redacted> On Behalf Of
Magnus Karlsson
Sent: Friday, March 19, 2021 3:14 PM
To: Karlsson, Magnus <magnus.karlsson@intel.com>; intel-wired-
lan@lists.osuosl.org; Nguyen, Anthony L [off-list ref];
Fijalkowski, Maciej [off-list ref]
Cc: netdev@vger.kernel.org; Joshi, Sreedevi <redacted>
Subject: [Intel-wired-lan] [PATCH intel-net] i40e: fix receiving of single packets
in xsk zero-copy mode

From: Magnus Karlsson <magnus.karlsson@intel.com>

Fix so that single packets are received immediately instead of in batches of 8.
If you sent 1 pss to a system, you received 8 packets every 8 seconds instead
of 1 packet every second. The problem behind this was that the work_done
reporting from the Tx part of the driver was broken. The work_done
reporting in i40e controls not only the reporting back to the napi logic but
also the setting of the interrupt throttling logic. When Tx or Rx reports that it
has more to do, interrupts are throttled or coalesced and when they both
report that they are done, interrupts are armed right away. If the wrong
work_done value is returned, the logic will start to throttle interrupts in a
situation where it should have just enabled them. This leads to the undesired
batching behavior seen in user-space.

Fix this by returning the correct boolean value from the Tx xsk zero-copy
path. Return true if there is nothing to do or if we got fewer packets to
process than we asked for. Return false if we got as many packets as the
budget since there might be more packets we can process.

Fixes: 3106c580fb7c ("i40e: Use batched xsk Tx interfaces to increase
performance")
Reported-by: Sreedevi Joshi <redacted>
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
---
 drivers/net/ethernet/intel/i40e/i40e_xsk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Tested-by: Kiran Bhandare <redacted>  A Contingent Worker at Intel