Subject: Re: [PATCH net 1/1] net: stmmac: add fsleep() in HW Rx timestamp checking loop

From: Jakub Kicinski <[email-masked]>
Date: Thu, 14 Apr 2022 10:42:59 +0200

On Thu, 14 Apr 2022 15:29:34 +0800 Tan Tee Min wrote:
> > > --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
> > > +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
> > > @@ -279,10 +279,11 @@ static int dwmac4_wrback_get_rx_timestamp_status(void *desc, void *next_desc,
> > >  			/* Check if timestamp is OK from context descriptor */
> > >  			do {
> > >  				ret = dwmac4_rx_check_timestamp(next_desc);
> > > -				if (ret < 0)
> > > +				if (ret <= 0)
> > >  					goto exit;
> > >  				i++;
> > >  
> > > +				fsleep(1);  
> > 
> > This is nutty.  Why isn't this code using proper deferral mechanisms
> > like work or kthread?  
> 
> Appreciate your comment.
> The dwmac4_wrback_get_rx_timestamp_status() is called by stmmac_rx()
> function which is scheduled by NAPI framework.
> Do we still need to create deferred work inside NAPI work?
> Would you mind to explain it more in detail?

fsleep() is a big hammer, can you try cpu_relax() and bumping the max
loop count a little?