linux-kernel - Re: [PATCH 1/5] vdso/gettimeofday: Clarify comment about open coded function

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Date: Mon, 1 Jul 2024 15:58:13 +0100
From: Vincenzo Frascino <vincenzo.frascino@....com>
To: Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] vdso/gettimeofday: Clarify comment about open coded
 function



On 01/07/2024 15:47, Anna-Maria Behnsen wrote:
> The two comments state, that the following code open codes something but
> they lack to specify what exactly is open coded.
> 
> Expand comments by mentioning the reference to the open coded function.
> 
> Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>

> ---
>  lib/vdso/gettimeofday.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
> index 899850bd6f0b..c01eaafd8041 100644
> --- a/lib/vdso/gettimeofday.c
> +++ b/lib/vdso/gettimeofday.c
> @@ -140,14 +140,14 @@ static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk,
>  
>  	do {
>  		/*
> -		 * Open coded to handle VDSO_CLOCKMODE_TIMENS. Time namespace
> -		 * enabled tasks have a special VVAR page installed which
> -		 * has vd->seq set to 1 and vd->clock_mode set to
> -		 * VDSO_CLOCKMODE_TIMENS. For non time namespace affected tasks
> -		 * this does not affect performance because if vd->seq is
> -		 * odd, i.e. a concurrent update is in progress the extra
> -		 * check for vd->clock_mode is just a few extra
> -		 * instructions while spin waiting for vd->seq to become
> +		 * Open coded function vdso_read_begin() to handle
> +		 * VDSO_CLOCKMODE_TIMENS. Time namespace enabled tasks have a
> +		 * special VVAR page installed which has vd->seq set to 1 and
> +		 * vd->clock_mode set to VDSO_CLOCKMODE_TIMENS. For non time
> +		 * namespace affected tasks this does not affect performance
> +		 * because if vd->seq is odd, i.e. a concurrent update is in
> +		 * progress the extra check for vd->clock_mode is just a few
> +		 * extra instructions while spin waiting for vd->seq to become
>  		 * even again.
>  		 */
>  		while (unlikely((seq = READ_ONCE(vd->seq)) & 1)) {
> @@ -223,8 +223,8 @@ static __always_inline int do_coarse(const struct vdso_data *vd, clockid_t clk,
>  
>  	do {
>  		/*
> -		 * Open coded to handle VDSO_CLOCK_TIMENS. See comment in
> -		 * do_hres().
> +		 * Open coded function vdso_read_begin() to handle
> +		 * VDSO_CLOCK_TIMENS. See comment in do_hres().
>  		 */
>  		while ((seq = READ_ONCE(vd->seq)) & 1) {
>  			if (IS_ENABLED(CONFIG_TIME_NS) &&
> 

-- 
Regards,
Vincenzo