[patch 27/44] posix-cpu-timers: Provide array based access to expiry cache

Thomas Gleixner
2019-08-19T15:46:04Z

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>
---
include/linux/posix-timers.h | 26 +++++++++++++++++++-------
include/linux/sched/types.h | 4 ++--
kernel/time/posix-cpu-timers.c | 10 ++++++++++
3 files changed, 31 insertions(+), 9 deletions(-)

--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -65,27 +65,39 @@ static inline int clockid_to_fd(const cl
/*
* 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]);
@@ -96,13 +108,13 @@ static inline void posix_cputimers_group
{
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;
}

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 */
--- a/include/linux/sched/types.h
+++ b/include/linux/sched/types.h
@@ -4,8 +4,8 @@

/**
* 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
@@ -13,8 +13,8 @@
* 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;
};

--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -18,6 +18,16 @@

#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);

/*