> -----Original Message-----
> From: petter@xxxxxxxxxx <petter@xxxxxxxxxx>
> Sent: Tuesday, May 30, 2023 9:09 PM
> To: kvalo@xxxxxxxxxx
> Cc: Larry.Finger@xxxxxxxxxxxx; andreas@xxxxxxxx; iam@xxxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx;
> linux-wireless@xxxxxxxxxxxxxxx; linux@xxxxxxxxxxxxx; petter.mabacker@xxxxxxx; petter@xxxxxxxxxx; Ping-Ke
> Shih <pkshih@xxxxxxxxxxx>; s.hauer@xxxxxxxxxxxxxx
> Subject: Re: [PATCH] wifi: rtw88: usb: Make work queues high prio
>
> petter@xxxxxxxxxx writes:
>
> >> From: Petter Mabacker <petter.mabacker@xxxxxxx>
> >>
> >> The rtw8822cu driver have problem to handle high rx or tx rates compared
> >> with high load (such as high I/O) on slower systems, such as for example
> >> i.MX6 SoloX and similar platforms.
> >>
> >> The problems are more frequent when having the access point close to the
> >> device. On slower systems it's often enough to download a large file,
> >> combined with generating I/O load to trigger:
> >>
> >> [ 374.763424] rtw_8822cu 1-1.2:1.2: failed to get tx report from firmware
> >> [ 377.771790] rtw_8822cu 1-1.2:1.2: failed to send h2c command
> >> [ 407.813460] rtw_8822cu 1-1.2:1.2: firmware failed to report density after scan
> >> [ 414.965826] rtw_8822cu 1-1.2:1.2: failed to send h2c command
> >> [ 444.993462] rtw_8822cu 1-1.2:1.2: firmware failed to report density after scan
> >> [ 452.144551] rtw_8822cu 1-1.2:1.2: failed to send h2c command
> >> [ 482.183445] rtw_8822cu 1-1.2:1.2: firmware failed to report density after scan
> >> [ 489.426263] rtw_8822cu 1-1.2:1.2: failed to send h2c command
> >>
> >> Another way is to simply perform a wifi rescan.
> >>
> >> Benchmarking shows that setting a high prio workqueue for tx/rx will
> >> significally improve things. Also compared alloc_workqueue with
> >> alloc_ordered_workqueue, but even thou the later seems to slightly
> >> improve things it's still quite easy to reproduce the above issues. So
> >> that leads to the decision to go for alloc_workqueue.
> >>
> >> Thanks to Ping-Ke Shih <pkshih@xxxxxxxxxxx> that came up with the idea
> >> of exploring tweaking of the work queue's within a similar discussion.
> >>
> >> Fixes: a82dfd33d1237 ("wifi: rtw88: Add common USB chip support")
> >> Signed-off-by: Petter Mabacker <petter.mabacker@xxxxxxx>
> >> ---
> >> drivers/net/wireless/realtek/rtw88/usb.c | 4 ++--
> >> 1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/net/wireless/realtek/rtw88/usb.c b/drivers/net/wireless/realtek/rtw88/usb.c
> >> index 44a5fafb9905..bfe0845528ec 100644
> >> --- a/drivers/net/wireless/realtek/rtw88/usb.c
> >> +++ b/drivers/net/wireless/realtek/rtw88/usb.c
> >> @@ -716,7 +716,7 @@ static int rtw_usb_init_rx(struct rtw_dev *rtwdev)
> >> struct rtw_usb *rtwusb = rtw_get_usb_priv(rtwdev);
> >> int i;
> >>
> >> - rtwusb->rxwq = create_singlethread_workqueue("rtw88_usb: rx wq");
> >> + rtwusb->rxwq = alloc_workqueue("rtw88_usb: rx wq", WQ_UNBOUND | WQ_HIGHPRI, 0);
> >> if (!rtwusb->rxwq) {
> >> rtw_err(rtwdev, "failed to create RX work queue\n");
> >> return -ENOMEM;
> >> @@ -750,7 +750,7 @@ static int rtw_usb_init_tx(struct rtw_dev *rtwdev)
> >> struct rtw_usb *rtwusb = rtw_get_usb_priv(rtwdev);
> >> int i;
> >>
> >> - rtwusb->txwq = create_singlethread_workqueue("rtw88_usb: tx wq");
> >> + rtwusb->txwq = alloc_workqueue("rtw88_usb: tx wq", WQ_UNBOUND | WQ_HIGHPRI, 0);
> >> if (!rtwusb->txwq) {
> >> rtw_err(rtwdev, "failed to create TX work queue\n");
> >> return -ENOMEM;
>
> >Should this workqueue be ordered or not? Please check Tejun's patchset
> >about using ordered queues:
>
> >https://lore.kernel.org/lkml/20230421025046.4008499-1-tj@xxxxxxxxxx/
>
> Thanks for pointing out this interesting patchset. As described in the
> commit msg, I did play around with alloc_ordered_workqueue. But at least
> on the slower systems I tested it on (i.MX6 SoloX and BCM2835) it worked
> a bit better, but I was still able to reproduce the above mention issue.
> So I tried to instead use alloc_workqueue and set max_active=0 and that
> seems to be enough to make things a lot more stable.
>
> However after reading Tejun's patchet I'm very intersted of feedback if
> you or someone else have comments about using alloc_workqueue with
> max_active=0 , or if this can give some other issues? It seems to work
> fine for me when running it also on a i.MX8 multicore system.
>
Both rtwusb->rxwq and rtwusb->txwq are only queued single one work respectively,
so I thought alloc_workqueue() and alloc_ordered_workqueue() would get the same
results, but it seems not. That is a little weird to me.
I'm not familiar with workqueue, but I think we can bisect arguments to address
what impact the results.
First we can expand macro alloc_ordered_workqueue() below
rtwusb->txwq = alloc_ordered_workqueue("rtw88_usb: tx wq", WQ_HIGHPRI);
into
rtwusb->txwq = alloc_workqueue("rtw88_usb: tx wq",
WQ_UNBOUND | __WQ_ORDERED | __WQ_ORDERED_EXPLICIT |
WQ_HIGHPRI, 1);
Secondly, compare the one you are using:
rtwusb->txwq = alloc_workqueue("rtw88_usb: tx wq", WQ_UNBOUND | WQ_HIGHPRI, 0);
Then, we can align the arguments one-by-one to know which argument dominates
the result.
Ping-Ke
