Re: [PATCH 2/4] iopoll: Avoid evaluating 'cond' twice in poll_timeout_us()

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 03 Jul 2025, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Currently poll_timeout_us() evaluates 'cond' twice at the end
> of the success case. This not desirable in case 'cond' itself
> is expensive.
>
> Avoid the double evaluation by tracking the return value in
> a variable. Need to use a triple undescore '___ret' name to
> avoid a conflict with an existing double undescore '__ret'
> variable in the regmap code.
>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Cc: Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian@intel.com>
> Cc: Imre Deak <imre.deak@intel.com>
> Cc: David Laight <david.laight.linux@gmail.com>
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> Cc: Matt Wagantall <mattw@codeaurora.org>
> Cc: Dejin Zheng <zhengdejin5@gmail.com>
> Cc: intel-gfx@lists.freedesktop.org
> Cc: intel-xe@lists.freedesktop.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  include/linux/iopoll.h | 22 ++++++++++++++++++----
>  1 file changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/iopoll.h b/include/linux/iopoll.h
> index 0d8186d3df03..69296e6adbf3 100644
> --- a/include/linux/iopoll.h
> +++ b/include/linux/iopoll.h
> @@ -36,23 +36,30 @@
>  	u64 __timeout_us = (timeout_us); \
>  	unsigned long __sleep_us = (sleep_us); \
>  	ktime_t __timeout = ktime_add_us(ktime_get(), __timeout_us); \
> +	int ___ret; \
>  	might_sleep_if((__sleep_us) != 0); \
>  	if ((sleep_before_op) && __sleep_us) \
>  		usleep_range((__sleep_us >> 2) + 1, __sleep_us); \
>  	for (;;) { \
>  		op; \
> -		if (cond) \
> +		if (cond) { \
> +			___ret = 0; \
>  			break; \
> +		} \
>  		if (__timeout_us && \
>  		    ktime_compare(ktime_get(), __timeout) > 0) { \
>  			op; \
> +			if (cond) \
> +				___ret = 0; \
> +			else \
> +				___ret = -ETIMEDOUT; \
>  			break; \
>  		} \
>  		if (__sleep_us) \
>  			usleep_range((__sleep_us >> 2) + 1, __sleep_us); \
>  		cpu_relax(); \
>  	} \
> -	(cond) ? 0 : -ETIMEDOUT; \
> +	___ret; \
>  })
>  
>  /**
> @@ -83,6 +90,7 @@
>  	s64 __left_ns = __timeout_us * NSEC_PER_USEC; \
>  	unsigned long __delay_us = (delay_us); \
>  	u64 __delay_ns = __delay_us * NSEC_PER_USEC; \
> +	int ___ret; \
>  	if ((delay_before_op) && __delay_us) { \
>  		udelay(__delay_us); \
>  		if (__timeout_us) \
> @@ -90,10 +98,16 @@
>  	} \
>  	for (;;) { \
>  		op; \
> -		if (cond) \
> +		if (cond) { \
> +			___ret = 0; \
>  			break; \
> +		} \
>  		if (__timeout_us && __left_ns < 0) { \
>  			op; \
> +			if (cond) \
> +				___ret = 0; \
> +			else \
> +				___ret = -ETIMEDOUT; \
>  			break; \
>  		} \
>  		if (__delay_us) { \
> @@ -105,7 +119,7 @@
>  		if (__timeout_us) \
>  			__left_ns--; \
>  	} \
> -	(cond) ? 0 : -ETIMEDOUT; \
> +	___ret; \
>  })
>  
>  /**

-- 
Jani Nikula, Intel