sched: keep utime/stime monotonic

sched: keep utime/stime monotonic

cpustats use utime/stime as a ratio against sum_exec_runtime, as a
consequence it can happen - when the ratio changes faster than time
accumulates - that either can be appear to go backwards.

Combined backport for 2.6.23 of the following patches from mainline:
commit 73a2bcb0edb9ffb0b007b3546b430e2c6e415eee
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
  sched: keep utime/stime monotonic

commit 9301899be75b464ef097f0b5af7af6d9bd8f68a7
Author: Balbir Singh <balbir@linux.vnet.ibm.com>
  sched: fix /proc/<PID>/stat stime/utime monotonicity, part 2

Signed-off-by: Frans Pop <elendil@planet.nl>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/proc/array.c b/fs/proc/array.c
index ee4814dd98f9cb5745e2195db44ade96b85cdd5d..20d7ae4582e26b233cc99c6f447b82080e55f08b 100644 (file)
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -351,7 +351,8 @@ static cputime_t task_utime(struct task_struct *p)
        }
        utime = (clock_t)temp;
 
-       return clock_t_to_cputime(utime);
+       p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime));
+       return p->prev_utime;
 }
 
 static cputime_t task_stime(struct task_struct *p)
@@ -366,7 +367,8 @@ static cputime_t task_stime(struct task_struct *p)
        stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
                        cputime_to_clock_t(task_utime(p));
 
-       return clock_t_to_cputime(stime);
+       p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+       return p->prev_stime;
 }
 #endif
 

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 313c6b6e774f887438c3926c539186ed03e6939e..f509fbd97df9799eccdc27730897804cab6adc22 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1022,6 +1022,7 @@ struct task_struct {
 
        unsigned int rt_priority;
        cputime_t utime, stime;
+       cputime_t prev_utime, prev_stime;
        unsigned long nvcsw, nivcsw; /* context switch counts */
        struct timespec start_time;             /* monotonic time */
        struct timespec real_start_time;        /* boot based time */

diff --git a/kernel/fork.c b/kernel/fork.c
index 33f12f48684a0053a82d72506c1d7ec1e7ca6a15..f299d4522a2d190a16bcf55b4d4c38b6e508d1a4 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1045,6 +1045,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 
        p->utime = cputime_zero;
        p->stime = cputime_zero;
+       p->prev_utime = cputime_zero;
+       p->prev_stime = cputime_zero;
 
 #ifdef CONFIG_TASK_XACCT
        p->rchar = 0;           /* I/O counter: bytes read */