net: ti: icssg-prueth: Fix AF_XDP fill ring alloc and wakeup condition

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emac_rx_packet_zc() calls prueth_rx_alloc_zc() with count (frames
received in the current NAPI poll) as the allocation budget.  Two
problems arise from this:

1. When the CPPI5 descriptor pool is exhausted (avail_desc == 0,
   FDQ already holds the maximum number of descriptors), count > 0
   still triggers allocation attempts that all fail, spamming the
   kernel log with "rx push: failed to allocate descriptor" at
   high packet rates.

2. The XSK wakeup condition "ret < count" is wrong when avail_desc
   is zero: ret == 0 and count can be up to 64, so the condition is
   always true.  This causes ~200 spurious ndo_xsk_wakeup() calls
   per second even when the FDQ is already full, wasting CPU cycles
   in repeated NAPI invocations that process zero frames.

Fix both by introducing alloc_budget = min(budget, avail_desc):
- When avail_desc == 0 no allocation is attempted, avoiding pool
  exhaustion errors.  The wakeup condition "ret < alloc_budget"
  evaluates to 0 < 0 == false, correctly clearing the wakeup flag
  so the hardware IRQ re-arms NAPI without spurious kicks.
- In steady state avail_desc == count <= budget, so alloc_budget
  == count and behaviour is unchanged.
- After a dry-ring stall (count == 0, avail_desc > 0), alloc_budget
  > 0 causes new descriptors to be posted to the FDQ so the hardware
  can resume receiving immediately.

Fixes: 7a64bb388d ("net: ti: icssg-prueth: Add AF_XDP zero copy for RX")
Signed-off-by: Meghana Malladi <m-malladi@ti.com>
Link: https://patch.msgid.link/20260611185744.2498070-2-m-malladi@ti.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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Meghana Malladi 2026-06-12 00:27:41 +05:30 • committed by Jakub Kicinski

parent c66f8511a8

commit dfb787f7d1

1 changed files with 6 additions and 8 deletions

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drivers/net/ethernet/ti/icssg/icssg_common.c

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