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posix-cpu-timers: Provide array based access to expiry cache 

Using struct task_cputime for the expiry cache is a pretty odd choice and
comes with magic defines to rename the fields for usage in the expiry
cache.

struct task_cputime is basically a u64 array with 3 members, but it has
distinct members.

The expiry cache content is different than the content of task_cputime
because

  expiry[PROF]  = task_cputime.stime + task_cputime.utime
  expiry[VIRT]  = task_cputime.utime
  expiry[SCHED] = task_cputime.sum_exec_runtime

So there is no direct mapping between task_cputime and the expiry cache and
the #define based remapping is just a horrible hack.

Having the expiry cache array based allows further simplification of the
expiry code.

To avoid an all in one cleanup which is hard to review add a temporary
anonymous union into struct task_cputime which allows array based access to
it. That requires to reorder the members. Add a build time sanity check to
validate that the members are at the same place.

The union and the build time checks will be removed after conversion.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190821192921.105793824@linutronix.de
This commit is contained in:
Thomas Gleixner 2019-08-21 21:09:07 +02:00
parent 3a245c0f11
commit 11b8462f7e
3 changed files with 31 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
include/linux/posix-timers.h
View File

@ -65,27 +65,39 @@ static inline int clockid_to_fd(const clockid_t clk)
/*
* Alternate field names for struct task_cputime when used on cache
* expirations. Will go away soon.
*
* stime corresponds to CLOCKCPU_PROF
* utime corresponds to CLOCKCPU_VIRT
* sum_exex_runtime corresponds to CLOCKCPU_SCHED
*
* The ordering is currently enforced so struct task_cputime and the
* expiries array in struct posix_cputimers are equivalent.
*/
#define virt_exp utime
#define prof_exp stime
#define virt_exp utime
#define sched_exp sum_exec_runtime
#ifdef CONFIG_POSIX_TIMERS
/**
* posix_cputimers - Container for posix CPU timer related data
* @cputime_expires: Earliest-expiration cache
* @cputime_expires: Earliest-expiration cache task_cputime based
* @expiries: Earliest-expiration cache array based
* @cpu_timers: List heads to queue posix CPU timers
*
* Used in task_struct and signal_struct
*/
struct posix_cputimers {
struct task_cputime cputime_expires;
struct list_head cpu_timers[CPUCLOCK_MAX];
/* Temporary union until all users are cleaned up */
union {
struct task_cputime cputime_expires;
u64 expiries[CPUCLOCK_MAX];
};
struct list_head cpu_timers[CPUCLOCK_MAX];
};
static inline void posix_cputimers_init(struct posix_cputimers *pct)
{
memset(&pct->cputime_expires, 0, sizeof(pct->cputime_expires));
memset(&pct->expiries, 0, sizeof(pct->expiries));
INIT_LIST_HEAD(&pct->cpu_timers[0]);
INIT_LIST_HEAD(&pct->cpu_timers[1]);
INIT_LIST_HEAD(&pct->cpu_timers[2]);
@ -96,7 +108,7 @@ void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit);
static inline void posix_cputimers_rt_watchdog(struct posix_cputimers *pct,
u64 runtime)
{
pct->cputime_expires.sched_exp = runtime;
pct->expiries[CPUCLOCK_SCHED] = runtime;
}
/* Init task static initializer */

4
include/linux/sched/types.h
View File

@ -6,8 +6,8 @@
/**
* struct task_cputime - collected CPU time counts
* @utime: time spent in user mode, in nanoseconds
* @stime: time spent in kernel mode, in nanoseconds
* @utime: time spent in user mode, in nanoseconds
* @sum_exec_runtime: total time spent on the CPU, in nanoseconds
*
* This structure groups together three kinds of CPU time that are tracked for
@ -15,8 +15,8 @@
* these counts together and treat all three of them in parallel.
*/
struct task_cputime {
u64 utime;
u64 stime;
u64 utime;
unsigned long long sum_exec_runtime;
};

12
kernel/time/posix-cpu-timers.c
View File

@ -18,13 +18,23 @@
#include "posix-timers.h"
static inline void temporary_check(void)
{
BUILD_BUG_ON(offsetof(struct task_cputime, stime) !=
CPUCLOCK_PROF * sizeof(u64));
BUILD_BUG_ON(offsetof(struct task_cputime, utime) !=
CPUCLOCK_VIRT * sizeof(u64));
BUILD_BUG_ON(offsetof(struct task_cputime, sum_exec_runtime) !=
CPUCLOCK_SCHED * sizeof(u64));
}
static void posix_cpu_timer_rearm(struct k_itimer *timer);
void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit)
{
posix_cputimers_init(pct);
if (cpu_limit != RLIM_INFINITY)
pct->cputime_expires.prof_exp = cpu_limit * NSEC_PER_SEC;
pct->expiries[CPUCLOCK_PROF] = cpu_limit * NSEC_PER_SEC;
}
/*