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SubjectRe: [PATCH] PM: fix calculation mistake in roll-over cases
Date
On Tuesday, October 25, 2011, vbyravarasu@nvidia.com wrote:
> From: venu byravarasu <vbyravarasu@nvidia.com>
>
> In case of jiffies roll over, delta is made zero.
> Hence fixing it, after taking roll over into consideration.
>
> Signed-off-by: venu byravarasu <vbyravarasu@nvidia.com>
> ---
> When jiffies roll over, calculation of time spent in the
> current state (stored in variable 'delta') is incorrect.
> Hence fixing it, after taking roll over into consideration.
>
> drivers/base/power/runtime.c | 7 ++++---
> 1 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 1079e03..bd93fb0 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -30,12 +30,13 @@ static int rpm_suspend(struct device *dev, int rpmflags);
> void update_pm_runtime_accounting(struct device *dev)
> {
> unsigned long now = jiffies;
> - int delta;
> + unsigned long delta;
> + unsigned long max_num = ~0;
>
> delta = now - dev->power.accounting_timestamp;
>
> - if (delta < 0)
> - delta = 0;
> + if (now < dev->power.accounting_timestamp)
> + delta = max_num - dev->power.accounting_timestamp + now;
>
> dev->power.accounting_timestamp = now;

I'm not sure how this is supposed to improve things. Care to give more
details?

Rafael


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