From: Mark Kettenis <mark.kettenis@xs4all.nl>
Subject: Re: acpiec: try a short busy-wait first
To: joshua stein <jcs@jcs.org>
Cc: tech@openbsd.org
Date: Tue, 11 Nov 2025 17:04:37 +0100

> 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?

> 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);
> 
>