On Wed, 25 Nov 2015, Arnd Bergmann wrote:
> The following patch replaces all instances of time_t with time64_t i.e.
> change the type used for representing time from 32-bit to 64-bit. All
> 32-bit kernels to date use a signed 32-bit time_t type, which can only
> represent time until January 2038. Since embedded systems running 32-bit
> Linux are going to survive beyond that date, we have to change all
> current uses, in a backwards compatible way.
>
> The patch also changes the function get_seconds() that returns a 32-bit
> integer to ktime_get_seconds() that returns seconds as 64-bit integer.
>
> The patch changes the type of ticks from time_t to u32. We keep ticks as
> 32-bits as the function uses 32-bit arithmetic which would prove less
> expensive than 64-bit arithmetic and the function is expected to be
> called atleast once every 32 seconds.
>
> Signed-off-by: Heena Sirwani <heenasirwani@xxxxxxxxx>
> Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> This is an older patch I still had in my queue. Who should pick it up?
Tejun, Cc'ed
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 10ae73611d80..c9ea63ff70a7 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -51,6 +51,7 @@
> #include <linux/stat.h>
> #include <linux/string.h>
> #include <linux/time.h>
> +#include <linux/time64.h>
> #include <linux/backing-dev.h>
> #include <linux/sort.h>
>
> @@ -68,7 +69,7 @@ struct static_key cpusets_enabled_key __read_mostly = STATIC_KEY_INIT_FALSE;
> struct fmeter {
> int cnt; /* unprocessed events count */
> int val; /* most recent output value */
> - time_t time; /* clock (secs) when val computed */
> + time64_t time; /* clock (secs) when val computed */
> spinlock_t lock; /* guards read or write of above */
> };
>
> @@ -1374,7 +1375,7 @@ out:
> */
>
> #define FM_COEF 933 /* coefficient for half-life of 10 secs */
> -#define FM_MAXTICKS ((time_t)99) /* useless computing more ticks than this */
> +#define FM_MAXTICKS ((u32)99) /* useless computing more ticks than this */
> #define FM_MAXCNT 1000000 /* limit cnt to avoid overflow */
> #define FM_SCALE 1000 /* faux fixed point scale */
>
> @@ -1390,8 +1391,11 @@ static void fmeter_init(struct fmeter *fmp)
> /* Internal meter update - process cnt events and update value */
> static void fmeter_update(struct fmeter *fmp)
> {
> - time_t now = get_seconds();
> - time_t ticks = now - fmp->time;
> + time64_t now;
> + u32 ticks;
> +
> + now = ktime_get_seconds();
> + ticks = now - fmp->time;
>
> if (ticks == 0)
> return;
>
>
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