Re: [RFC PATCH 82/86] treewide: mtd: remove cond_resched()

[Miquel Raynal]

Hello,

rostedt@xxxxxxxxxxx wrote on Wed, 8 Nov 2023 12:21:16 -0500:

> On Wed, 8 Nov 2023 16:32:36 +0000
> Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> 
> > On Wed, Nov 08, 2023 at 05:28:27PM +0100, Miquel Raynal wrote:  
> > > > --- a/drivers/mtd/nand/raw/nand_legacy.c
> > > > +++ b/drivers/mtd/nand/raw/nand_legacy.c
> > > > @@ -203,7 +203,13 @@ void nand_wait_ready(struct nand_chip *chip)
> > > >  	do {
> > > >  		if (chip->legacy.dev_ready(chip))
> > > >  			return;
> > > > -		cond_resched();
> > > > +		/*
> > > > +		 * Use a cond_resched_stall() to avoid spinning in
> > > > +		 * a tight loop.
> > > > +		 * Though, given that the timeout is in milliseconds,
> > > > +		 * maybe this should timeout or event wait?    
> > > 
> > > Event waiting is precisely what we do here, with the hardware access
> > > which are available in this case. So I believe this part of the comment
> > > (in general) is not relevant. Now regarding the timeout I believe it is
> > > closer to the second than the millisecond, so timeout-ing is not
> > > relevant either in most cases (talking about mtd/ in general).    
> > 
> > I think you've misunderstood what Ankur wrote here.  What you're
> > currently doing is spinning in a very tight loop.  The comment is
> > suggesting you might want to msleep(1) or something to avoid burning CPU
> > cycles.  It'd be even better if the hardware could signal you somehow,
> > but I bet it can't.

Well, I think I'm aligned with the change and the first sentence in the
comment, but not with the second sentence which I find not relevant.

Maybe I don't understand what "maybe this should timeout" and Ankur
meant "sleeping" there, but for me a timeout is when you bail out with
an error. If sleeping is advised, then why not using a more explicit
wording? As for hardware events, in this case it is not relevant, as
you noticed, so I asked this part of the sentence to be dropped.

This is a legacy part of the core but is still part of the core. In
general I don't mind treewide changes to be slightly generic and I will
not be bothered too much with the device drivers changes, but the core
is more important to my eyes.

> Oh how I wish we could bring back the old PREEMPT_RT cpu_chill()...
> 
> #define cpu_chill()	msleep(1)

:')

Thanks,
Miquèl