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sched/cputime: Guarantee stime + utime == rtime

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While the current code guarantees monotonicity for stime and utime
independently of one another, it does not guarantee that the sum of
both is equal to the total time we started out with.

This confuses things (and peoples) who look at this sum, like top, and
will report >100% usage followed by a matching period of 0%.

Rework the code to provide both individual monotonicity and a coherent
sum.

Suggested-by: Fredrik Markstrom <fredrik.markstrom@gmail.com>
Reported-by: Fredrik Markstrom <fredrik.markstrom@gmail.com>
Tested-by: Fredrik Markstrom <fredrik.markstrom@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: jason.low2@hp.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2015-06-30 11:30:54 +02:00 • committed by Ingo Molnar
parent 781b020342
commit 9d7fb04276
4 changed files with 98 additions and 62 deletions
Download patch file Download diff file Expand all files Collapse all files

10
include/linux/init_task.h
View file

@ -32,6 +32,14 @@ extern struct fs_struct init_fs;
#define INIT_CPUSET_SEQ(tsk)
#endif
#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
#define INIT_PREV_CPUTIME(x) .prev_cputime = { \
.lock = __RAW_SPIN_LOCK_UNLOCKED(x.prev_cputime.lock), \
},
#else
#define INIT_PREV_CPUTIME(x)
#endif
#define INIT_SIGNALS(sig) { \
.nr_threads = 1, \
.thread_head = LIST_HEAD_INIT(init_task.thread_node), \
@ -46,6 +54,7 @@ extern struct fs_struct init_fs;
.cputime_atomic = INIT_CPUTIME_ATOMIC, \
.running = 0, \
}, \
INIT_PREV_CPUTIME(sig) \
.cred_guard_mutex = \
__MUTEX_INITIALIZER(sig.cred_guard_mutex), \
}
@ -246,6 +255,7 @@ extern struct task_group root_task_group;
INIT_TASK_RCU_TASKS(tsk) \
INIT_CPUSET_SEQ(tsk) \
INIT_RT_MUTEXES(tsk) \
INIT_PREV_CPUTIME(tsk) \
INIT_VTIME(tsk) \
INIT_NUMA_BALANCING(tsk) \
INIT_KASAN(tsk) \