netdev - Re: [PATCH 02/10] rtw88: Drop rf

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Date:   Fri, 20 May 2022 08:54:35 +0200
From:   "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>
To:     Pkshih <pkshih@...ltek.com>
Cc:     "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "johannes@...solutions.net" <johannes@...solutions.net>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "neojou@...il.com" <neojou@...il.com>,
        "kvalo@...nel.org" <kvalo@...nel.org>,
        "tony0620emma@...il.com" <tony0620emma@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "martin.blumenstingl@...glemail.com" 
        <martin.blumenstingl@...glemail.com>,
        "linux@...i-kroll.de" <linux@...i-kroll.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 02/10] rtw88: Drop rf_lock

On Fri, May 20, 2022 at 03:49:06AM +0000, Pkshih wrote:
> On Wed, 2022-05-18 at 10:23 +0200, Sascha Hauer wrote:
> > The rtwdev->rf_lock spinlock protects the rf register accesses in
> > rtw_read_rf() and rtw_write_rf(). Most callers of these functions hold
> > rtwdev->mutex already with the exception of the callsites in the debugfs
> > code. The debugfs code doesn't justify an extra lock, so acquire the mutex
> > there as well before calling rf register accessors and drop the now
> > unnecessary spinlock.
> > 
> > Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
> > ---
> >  drivers/net/wireless/realtek/rtw88/debug.c | 11 +++++++++++
> >  drivers/net/wireless/realtek/rtw88/hci.h   |  9 +++------
> >  drivers/net/wireless/realtek/rtw88/main.c  |  1 -
> >  drivers/net/wireless/realtek/rtw88/main.h  |  3 ---
> >  4 files changed, 14 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/net/wireless/realtek/rtw88/debug.c
> > b/drivers/net/wireless/realtek/rtw88/debug.c
> > index 1a52ff585fbc7..ba5ba852efb8c 100644
> > --- a/drivers/net/wireless/realtek/rtw88/debug.c
> > +++ b/drivers/net/wireless/realtek/rtw88/debug.c
> > 
> 
> [...]
> 
> > @@ -523,6 +527,8 @@ static int rtw_debug_get_rf_dump(struct seq_file *m, void *v)
> >  	u32 addr, offset, data;
> >  	u8 path;
> >  
> > +	mutex_lock(&rtwdev->mutex);
> > +
> >  	for (path = 0; path < rtwdev->hal.rf_path_num; path++) {
> >  		seq_printf(m, "RF path:%d\n", path);
> >  		for (addr = 0; addr < 0x100; addr += 4) {
> > @@ -537,6 +543,8 @@ static int rtw_debug_get_rf_dump(struct seq_file *m, void *v)
> >  		seq_puts(m, "\n");
> >  	}
> >  
> > +	mutex_unlock(&rtwdev->mutex);
> > +
> >  	return 0;
> >  }
> > 
> 
> This will take time to dump all RF registers for debugging
> purpose. For PCI interface, I think this would be okay.
> Could you try to dump registers via debufs while you are
> using a USB WiFi device, such as play Youtube or download files...

I just did a ping and iperf test while doing a:

while true; do cat /sys/kernel/debug/ieee80211/phy0/rtw88/rf_dump ; done

The register dumping has no influence on neither the throughput or the
latency.

Adding some debugging to the mutex_lock also tells why: rtwdev->mutex
isn't acquired for normal rx/tx. It is only acquired every two seconds
or so.

So I would say adding the mutex_lock around the register dump is not a
problem. If latency is a concern we could still move the mutex_lock()
into the loop.

Sascha

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