On Mon, 2021-02-01 at 06:38 +0000, Pkshih wrote:

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-----Original Message-----
From: Brian Norris [mailto:briannorris@chromium.org]
Sent: Saturday, January 30, 2021 7:39 AM
To: Pkshih
Cc: Yan-Hsuan Chuang; Kalle Valo; linux-wireless; Bernie Huang
Subject: Re: [PATCH v4 3/8] rtw88: add napi support

On Thu, Jan 28, 2021 at 1:45 AM Pkshih [off-list ref] wrote:

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-----Original Message-----
From: Brian Norris [mailto:briannorris@chromium.org]
On Fri, Jan 15, 2021 at 1:26 AM Ping-Ke Shih [off-list ref] wrote:

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+static u32 rtw_pci_rx_napi(struct rtw_dev *rtwdev, struct rtw_pci

*rtwpci,

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                           u8 hw_queue)

...

Are you sure you don't want any locking in rtw_pci_rx_napi()?
Previously, you held irq_lock for the entirety of rtw_pci_rx_isr(),
but now all the RX work is being deferred to a NAPI context, without
any additional lock. IIUC, that means you can be both handling RX and
other ISR operations at the same time. Is that intentional?

irq_lock is used to protect TX ring->queue. The TX skb(s) are queued into

the

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queue, and unlink the skb until TX_OK_ISR is received. So, RX doesn't need

to

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hold this lock.

I could be misunderstanding your locking model, but IIUC, you're left
with zero locking between NAPI RX and all other operations (H2C, link
up/down -- including DMA free, etc.). irq_lock used to protect you
from that.

Sorry, I'm wrong. I think irq_lock is used to protect not only TX ring->queue
but also TX/RX rings. The RX ring rtwpci->rx_rings[RTW_RX_QUEUE_MPDU] is reset
by rtw_pci_reset_buf_desc() when pci_stop(), and napi_poll() also uses it to
know how many RX packets are needed to be received. Therefore, we plan to
use irq_lock to protect napi_poll(), and then see if it affects performance.

I change my mind, because using irq_lock to protect napi_poll causes deadlock.
I think that it's disallowed to hold a spin_lock_bh and call napi APIs that uses
RCU lock.

Then, I have another simple thinking -- enable NAPI only if interrupt is
enabled. Other operations with RX ring are working only if interrupt is
disabled. So, we don't need a lock to protect RX ring at all.

The irq_lock is still used to protect TX ring/queue, and now it also used
to protect switching IMR. Some comments are added to describe about this.

Above is implemented in v5.

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Ping-Ke