linux-kernel - Re: [PATCH 13/15] powerpc/rtas: Use fsleep() to minimize additional sleep duration

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Message-ID: <87cyli5lwa.fsf@mail.lhotse>
Date: Thu, 05 Sep 2024 22:24:05 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Anna-Maria Behnsen <anna-maria@...utronix.de>, Frederic Weisbecker
 <frederic@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Jonathan
 Corbet <corbet@....net>
Cc: linux-kernel@...r.kernel.org, Len Brown <len.brown@...el.com>, "Rafael
 J. Wysocki" <rafael@...nel.org>, Anna-Maria Behnsen
 <anna-maria@...utronix.de>, Nathan Lynch <nathanl@...ux.ibm.com>,
 linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 13/15] powerpc/rtas: Use fsleep() to minimize additional
 sleep duration

Anna-Maria Behnsen <anna-maria@...utronix.de> writes:
> When commit 38f7b7067dae ("powerpc/rtas: rtas_busy_delay() improvements")
> was introduced, documentation about proper usage of sleep realted functions
> was outdated.
>
...
> Use fsleep() directly instead of using an own heuristic for the best
> sleeping mechanism to use..

Thanks for tidying this up. I only learnt about fsleep() in the last ~year.

Two minor nits ...

> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index f7e86e09c49f..0794ca28e51e 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -1390,21 +1390,14 @@ bool __ref rtas_busy_delay(int status)
>  		 */
>  		ms = clamp(ms, 1U, 1000U);
>  		/*
> -		 * The delay hint is an order-of-magnitude suggestion, not
> -		 * a minimum. It is fine, possibly even advantageous, for
> -		 * us to pause for less time than hinted. For small values,
> -		 * use usleep_range() to ensure we don't sleep much longer
> -		 * than actually needed.
> -		 *
> -		 * See Documentation/timers/timers-howto.rst for
> -		 * explanation of the threshold used here. In effect we use
> -		 * usleep_range() for 9900 and 9901, msleep() for
> -		 * 9902-9905.
> +		 * The delay hint is an order-of-magnitude suggestion, not a
> +		 * minimum. It is fine, possibly even advantageous, for us to
> +		 * pause for less time than hinted. To make sure pause time will
> +		 * not be a way longer than requested independent of HZ
 
"not be way longer" reads better I think?

> +		 * configuration, use fsleep(). See fsleep() for detailes of
                                                                 ^
                                                                 details
> +		 * used sleeping functions.
>  		 */
> -		if (ms <= 20)
> -			usleep_range(ms * 100, ms * 1000);
> -		else
> -			msleep(ms);
> +		fsleep(ms * 1000);
>  		break;
>  	case RTAS_BUSY:
>  		ret = true;

Acked-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)


cheers