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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>
This commit is contained in:
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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14
drivers/net/ethernet/ti/icssg/icssg_common.c
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@ -927,6 +927,7 @@ static int emac_rx_packet_zc(struct prueth_emac *emac, u32 flow_id,
struct cppi5_host_desc_t *desc_rx;
struct prueth_swdata *swdata;
dma_addr_t desc_dma, buf_dma;
int avail_desc, alloc_budget;
struct xdp_buff *xdp;
int xdp_status = 0;
int count = 0;
@ -993,16 +994,13 @@ static int emac_rx_packet_zc(struct prueth_emac *emac, u32 flow_id,
if (xdp_status & ICSSG_XDP_REDIR)
xdp_do_flush();
/* Allocate xsk buffers from the pool for the "count" number of
* packets processed in order to be able to receive more packets.
*/
ret = prueth_rx_alloc_zc(emac, count);
avail_desc = k3_cppi_desc_pool_avail(rx_chn->desc_pool);
alloc_budget = min_t(int, budget, avail_desc);
ret = prueth_rx_alloc_zc(emac, alloc_budget);
if (xsk_uses_need_wakeup(rx_chn->xsk_pool)) {
/* If the user space doesn't provide enough buffers then it must
* explicitly wake up the kernel when new buffers are available
*/
if (ret < count)
if (ret < alloc_budget)
xsk_set_rx_need_wakeup(rx_chn->xsk_pool);
else
xsk_clear_rx_need_wakeup(rx_chn->xsk_pool);