Re: [PATCH] ACPI: Read TSC upon resume

[Greg KH <gregkh@suse.de>]

On Wed, Oct 06, 2010 at 04:15:19PM -0700, Sameer Nanda wrote:
> Read the TSC upon resuming and print it out. This is useful
> in helping figure out amount of time spent in the BIOS when
> resuming from suspend.
> 
> Change-Id: I1d6a32bd62421becddecd152d561763e5f3e1101

What is this tag for?  I don't think it matches anything the kernel
community wants, do you?

And are you always going to be printing this out?  Why do we want to
know this every time?


> Signed-off-by: Sameer Nanda <snanda@chromium.org>
> ---
>  drivers/acpi/sleep.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
> index c0fed2e..f0588fa 100644
> --- a/drivers/acpi/sleep.c
> +++ b/drivers/acpi/sleep.c
> @@ -214,6 +214,7 @@ static int acpi_suspend_enter(suspend_state_t pm_state)
>  	acpi_status status = AE_OK;
>  	unsigned long flags = 0;
>  	u32 acpi_state = acpi_target_sleep_state;
> +	u64 tsc;
>  
>  	ACPI_FLUSH_CPU_CACHE();
>  
> @@ -235,6 +236,9 @@ static int acpi_suspend_enter(suspend_state_t pm_state)
>  
>  	case ACPI_STATE_S3:
>  		do_suspend_lowlevel();
> +		rdtscll(tsc);
> +		printk(KERN_INFO "TSC at resume: %llu\n",
> +				(unsigned long long)tsc);

How long does this take, will it slow down resume?

thanks,

greg k-h