From: Claudio Jeker <cjeker@diehard.n-r-g.com>
Subject: Re: acpiec: try a short busy-wait first
To: Mark Kettenis <mark.kettenis@xs4all.nl>
Cc: joshua stein <jcs@jcs.org>, tech@openbsd.org
Date: Tue, 11 Nov 2025 17:10:05 +0100

On Tue, Nov 11, 2025 at 05:04:37PM +0100, Mark Kettenis wrote:
> > Date: Mon, 10 Nov 2025 21:12:47 -0600
> > From: joshua stein <jcs@jcs.org>
> > 
> > A single execution of acpisbs_read() does 1027 EC reads, 299 writes, 
> > and takes about 5980 milliseconds.  It has to do this on the ACPI 
> > task queue thread which means anything else behind it has to wait up 
> > to nearly 6 seconds to run.
> > 
> > If we busy-wait for a wee bit before falling back on tsleep, the 
> > same acpisbs function with the same number of EC reads/writes 
> > finishes in 125 milliseconds.
> 
> I guess doing this should be safe.  Before I give an ok; did you
> try using tsleep_nsec() with a shorter timeout?

I doubt that changes anything, tsleep_nsec still rounds up to 1 tick minimum.
 
> > diff --git sys/dev/acpi/acpiec.c sys/dev/acpi/acpiec.c
> > index e6add9e7ef0..fc490ecbd33 100644
> > --- sys/dev/acpi/acpiec.c
> > +++ sys/dev/acpi/acpiec.c
> > @@ -91,7 +91,8 @@ void
> >  acpiec_wait(struct acpiec_softc *sc, uint8_t mask, uint8_t val)
> >  {
> >  	static int acpiecnowait;
> > -	uint8_t		stat;
> > +	int tries = 0;
> > +	uint8_t	stat;
> >  
> >  	dnprintf(40, "%s: EC wait_ns for: %b == %02x\n",
> >  	    DEVNAME(sc), (int)mask,
> > @@ -100,7 +101,7 @@ acpiec_wait(struct acpiec_softc *sc, uint8_t mask, uint8_t val)
> >  	while (((stat = acpiec_status(sc)) & mask) != val) {
> >  		if (stat & EC_STAT_SCI_EVT)
> >  			sc->sc_gotsci = 1;
> > -		if (cold || (stat & EC_STAT_BURST))
> > +		if (cold || (stat & EC_STAT_BURST) || tries++ < 300)
> >  			delay(1);
> >  		else
> >  			tsleep(&acpiecnowait, PWAIT, "acpiec", 1);
> > 
> > 
> 

-- 
:wq Claudio