linux-kernel - [PATCH v3 0/2] Improve ath10k flush queue mechanism

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Message-Id: <cover.1729844329.git.repk@triplefau.lt>
Date: Fri, 25 Oct 2024 10:23:46 +0200
From: Remi Pommarel <repk@...plefau.lt>
To: ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Kalle Valo <kvalo@...nel.org>, Jeff Johnson <jjohnson@...nel.org>,
 Cedric Veilleux <veilleux.cedric@...il.com>,
 Vasanthakumar Thiagarajan <quic_vthiagar@...cinc.com>,
 Remi Pommarel <repk@...plefau.lt>
Subject: [PATCH v3 0/2] Improve ath10k flush queue mechanism

It has been reported [0] that a 3-4 seconds (actually up to 5 sec) of
radio silence could be observed followed by the error below on ath10k
devices:

 ath10k_pci 0000:04:00.0: failed to flush transmit queue (skip 0 ar-state 1): 0

This is due to how the TX queues are flushed in ath10k. When a STA is
removed, mac80211 need to flush queues [1], but because ath10k does not
have a lightweight .flush_sta operation, ieee80211_flush_queues() is
called instead effectively blocking the whole queue during the drain
causing this radio silence. Also because ath10k_flush() waits for all
queued to be emptied, not only the flushed ones it could more easily
take up to 5 seconds to finish making the whole situation worst.

The first patch of this series adds a .flush_sta operation to flush only
specific STA traffic avoiding the need to stop whole queues and should
be enough in itself to fix the reported issue.

The second patch of this series is a proposal to improve ath10k_flush so
that it will be less likely to timeout waiting for non related queues to
drain.

The abose kernel warning could still be observed (e.g. flushing a dead
STA) but should be now harmless.

[0]: https://lore.kernel.org/all/CA+Xfe4FjUmzM5mvPxGbpJsF3SvSdE5_wgxvgFJ0bsdrKODVXCQ@mail.gmail.com/
[1]: commit 0b75a1b1e42e ("wifi: mac80211: flush queues on STA removal")

V3:
  - Initialize empty to true to fix smatch error

V2:
  - Add Closes tag
  - Use atomic instead of spinlock for per sta pending frame counter
  - Call ath10k_htt_tx_sta_dec_pending within rcu
  - Rename pending_per_queue[] to num_pending_per_queue[]

Remi Pommarel (2):
  wifi: ath10k: Implement ieee80211 flush_sta callback
  wifi: ath10k: Flush only requested txq in ath10k_flush()

 drivers/net/wireless/ath/ath10k/core.h   |  2 +
 drivers/net/wireless/ath/ath10k/htt.h    | 11 +++-
 drivers/net/wireless/ath/ath10k/htt_tx.c | 49 +++++++++++++++-
 drivers/net/wireless/ath/ath10k/mac.c    | 75 ++++++++++++++++++++----
 drivers/net/wireless/ath/ath10k/txrx.c   | 11 ++--
 5 files changed, 127 insertions(+), 21 deletions(-)

-- 
2.40.0