linux-kernel - Re: [PATCH v2 3/4] hwmon: (sch56xx-common) Replace msleep() with usleep

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Message-ID: <3af7602a-1703-4ff2-3905-dfd35742dd90@roeck-us.net>
Date:   Mon, 31 Jan 2022 12:10:12 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Armin Wolf <W_Armin@....de>, hdegoede@...hat.com
Cc:     jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] hwmon: (sch56xx-common) Replace msleep() with
 usleep_range()

On 1/31/22 11:31, Armin Wolf wrote:
> msleep(1) will often sleep more than 20ms, slowing down sensor
> and watchdog reads/writes. Use usleep_range() as recommended
> in timers-howto.rst to fix that.
> 
> Tested on a Fujitsu Esprimo P720.
> 
> Signed-off-by: Armin Wolf <W_Armin@....de>
> ---
>   drivers/hwmon/sch56xx-common.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/sch56xx-common.c b/drivers/hwmon/sch56xx-common.c
> index 0172aa16dc0c..f66e1ed4b1aa 100644
> --- a/drivers/hwmon/sch56xx-common.c
> +++ b/drivers/hwmon/sch56xx-common.c
> @@ -139,7 +139,7 @@ static int sch56xx_send_cmd(u16 addr, u8 cmd, u16 reg, u8 v)
>   	/* EM Interface Polling "Algorithm" */
>   	for (i = 0; i < max_busy_polls + max_lazy_polls; i++) {
>   		if (i >= max_busy_polls)
> -			msleep(1);
> +			usleep_range(1, 2);

This replaces a 1-millisecond sleep with a 1-2 microsecond sleep.

Are you sure this is what you want to do ? Given that task switches typically
take several microseconds, the new code is pretty much identical to a busy
loop, and the maximum sleep time is reduced significantly.

Guenter

>   		/* Read Interrupt source Register */
>   		val = inb(addr + 8);
>   		/* Write Clear the interrupt source bits */
> --
> 2.30.2
>