Messages in this thread | | | From | Sameer Nanda <> | Date | Thu, 7 Oct 2010 10:58:10 -0700 | Subject | Re: [PATCH] ACPI: Read TSC upon resume |
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(resending as plain text, sorry if you got dupe messages)
On Wed, Oct 6, 2010 at 7:19 PM, Greg KH <gregkh@suse.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@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?
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 >
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