linux-kernel - Re: [PATCH] ACPI: Read TSC upon resume

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Message-ID: <AANLkTi=mjaojm-O2rbKRTpsqpKiSKjU+P2dGZmENd-jU@mail.gmail.com>
Date:	Thu, 7 Oct 2010 10:58:10 -0700
From:	Sameer Nanda <snanda@...omium.org>
To:	Greg KH <gregkh@...e.de>
Cc:	lenb@...nel.org, stefan.bader@...onical.com,
	brad.figg@...onical.com, apw@...onical.com,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPI: Read TSC upon resume

(resending as plain text, sorry if you got dupe messages)

On Wed, Oct 6, 2010 at 7:19 PM, Greg KH <gregkh@...e.de> wrote:
> 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?

Yeah, its not needed.  Let me resubmit the patch without this tag.

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

Yes, every time.  This helps track variance in BIOS resume times
within a single boot.

>
>> Signed-off-by: Sameer Nanda <snanda@...omium.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?

The impact is ~10us (as measured on an Intel Atom N455 @ 1.66Ghz).
Given that resume time is currently of the order of 1sec, its in the
noise range.

Thanks for the feedback!

>
> thanks,
>
> greg k-h
>



-- 
Sameer
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