Re: [PATCH 1/6] wifi: ath11k: avoid burning CPU in ath11k_debugfs_fw_stats_request()

[Kalle Valo <kvalo@kernel.org>]

Baochen Qiang <quic_bqiang@quicinc.com> writes:

> We get report [1] that CPU is running a hot loop in
> ath11k_debugfs_fw_stats_request():
>
> 94.60%     0.00%  i3status         [kernel.kallsyms]                 [k] do_syscall_64
>         |
>          --94.60%--do_syscall_64
>                    |
>                     --94.55%--__sys_sendmsg
>                               ___sys_sendmsg
>                               ____sys_sendmsg
>                               netlink_sendmsg
>                               netlink_unicast
>                               genl_rcv
>                               netlink_rcv_skb
>                               genl_rcv_msg
>                               |
>                                --94.55%--genl_family_rcv_msg_dumpit
>                                          __netlink_dump_start
>                                          netlink_dump
>                                          genl_dumpit
>                                          nl80211_dump_station
>                                          |
>                                           --94.55%--ieee80211_dump_station
>                                                     sta_set_sinfo
>                                                     |
>                                                      --94.55%--ath11k_mac_op_sta_statistics
>                                                                ath11k_debugfs_get_fw_stats
>                                                                |
>                                                                 --94.55%--ath11k_debugfs_fw_stats_request
>                                                                           |
>                                                                           |--41.73%--_raw_spin_lock_bh
>                                                                           |
>                                                                           |--22.74%--__local_bh_enable_ip
>                                                                           |
>                                                                           |--9.22%--_raw_spin_unlock_bh
>                                                                           |
>                                                                            --6.66%--srso_alias_safe_ret
>
> This is because, if for whatever reason ar->fw_stats_done is not set by
> ath11k_update_stats_event(), ath11k_debugfs_fw_stats_request() won't yield
> CPU before an up to 3s timeout.
>
> Add 100ms sleep to avoid CPU burning.
>
> Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.37
>
> Fixes: d5c65159f289 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
> Reported-by: Yury Vostrikov <mon@unformed.ru>
> Closes: https://lore.kernel.org/all/7324ac7a-8b7a-42a5-aa19-de52138ff638@app.fastmail.com/ # [1]
> Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
> ---
>  drivers/net/wireless/ath/ath11k/debugfs.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/net/wireless/ath/ath11k/debugfs.c b/drivers/net/wireless/ath/ath11k/debugfs.c
> index 57281a135dd7..a5e0f2092da5 100644
> --- a/drivers/net/wireless/ath/ath11k/debugfs.c
> +++ b/drivers/net/wireless/ath/ath11k/debugfs.c
> @@ -207,6 +207,9 @@ static int ath11k_debugfs_fw_stats_request(struct ath11k *ar,
>  			break;
>  		}
>  		spin_unlock_bh(&ar->data_lock);
> +
> +		/* 100ms is empirical, change if required */
> +		msleep(100);
>  	}
>  	return 0;
>  }

Please don't reinvent the wheel. Why not just use completion instead of
this ugly spinning hack?

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