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    SubjectRe: [PATCH] ACPI: Read TSC upon resume
    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


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