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

[Baochen Qiang]

On 11/13/2024 7:12 PM, Kalle Valo wrote:
> Baochen Qiang <quic_bqiang at 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 at unformed.ru>
>> Closes: https://lore.kernel.org/all/7324ac7a-8b7a-42a5-aa19-de52138ff638@app.fastmail.com/ # [1]
>> Signed-off-by: Baochen Qiang <quic_bqiang at 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?
previously I was thinking that a wait_for_completion() is not allowed since we are in atomic context due to spin_lock. But thinking it more I find that after changing to use completion, the spin_lock is not necessary. so thanks, will do in next version.

>