linux-kernel - Re: [PATCH] aoe: Use 64-bit timestamp in frame

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Date:	Mon, 11 May 2015 17:38:03 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Tina Ruchandani <ruchandani.tina@...il.com>
Cc:	"Ed L. Cashin" <ed.cashin@....org>, y2038@...ts.linaro.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] aoe: Use 64-bit timestamp in frame

On Monday 11 May 2015 08:05:05 Tina Ruchandani wrote:
> 'struct frame' uses two variables to store the sent timestamp - 'struct
> timeval' and jiffies. jiffies is used to avoid discrepancies caused by
> updates to system time. 'struct timeval' uses 32-bit representation for
> seconds which will overflow in year 2038.
> This patch does the following:
> - Replace the use of 'struct timeval' and jiffies with ktime_t, which
> is a 64-bit timestamp and is year 2038 safe.
> - ktime_t provides both long range (like jiffies) and high resolution
> (like timeval). Using ktime_get (monotonic time) instead of wall-clock
> time prevents any discprepancies caused by updates to system time.
> 
> Signed-off-by: Tina Ruchandani <ruchandani.tina@...il.com>

Very nice!

> @@ -499,32 +497,15 @@ resend(struct aoedev *d, struct frame *f)
>  static int
>  tsince_hr(struct frame *f)
>  {
> -	struct timeval now;
> +	ktime_t now;
>  	int n;
>  
> -	do_gettimeofday(&now);
> -	n = now.tv_usec - f->sent.tv_usec;
> -	n += (now.tv_sec - f->sent.tv_sec) * USEC_PER_SEC;
> +	now = ktime_get();
> +	n = ktime_to_us(ktime_sub(now, f->sent));
>  

I would cut four extra lines by writing this as

	return ktime_us_delta(ktime_get(), f->sent));

but the effect is exactly the same.

With that change, please add

Reviewed-by: Arnd Bergmann <arnd@...db.de>

	Arnd
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