Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=364e3a3d8a26aae058cf1c257457ad1f6b1cfe4c
Commit: 364e3a3d8a26aae058cf1c257457ad1f6b1cfe4c
Parent: 9fc89c2dea7ca7915e6606e49167cdca2f3c4e30
Author: Jeff Dike <[EMAIL PROTECTED]>
AuthorDate: Wed Nov 28 16:21:51 2007 -0800
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Thu Nov 29 09:24:53 2007 -0800
uml: fix !NO_HZ busy-loop
With NO_HZ disabled, the UML idle loop effectively becomes a busy loop, as
it will sleep for no time.
The cause was forgetting to restart the tick after waking up from sleep.
It was disabled before sleeping, and the remaining time used as the
interval to sleep. So, the tick needs to be restarted when nanosleep
finishes.
This is done by introducing after_sleep_interval, which is empty in the
NO_HZ case, but which sets the tick starting in the !NO_HZ case.
Signed-off-by: Jeff Dike <[EMAIL PROTECTED]>
Cc: Miklos Szeredi <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
arch/um/os-Linux/time.c | 54 ++++++++++++++++++++++++++++++++++++++++++++--
1 files changed, 51 insertions(+), 3 deletions(-)
diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index e34e1ef..ef02d94 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -59,7 +59,7 @@ long long disable_timer(void)
{
struct itimerval time = ((struct itimerval) { { 0, 0 }, { 0, 0 } });
- if(setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
+ if (setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
printk(UM_KERN_ERR "disable_timer - setitimer failed, "
"errno = %d\n", errno);
@@ -74,13 +74,61 @@ long long os_nsecs(void)
return timeval_to_ns(&tv);
}
+#ifdef UML_CONFIG_NO_HZ
+static int after_sleep_interval(struct timespec *ts)
+{
+}
+#else
+static inline long long timespec_to_us(const struct timespec *ts)
+{
+ return ((long long) ts->tv_sec * UM_USEC_PER_SEC) +
+ ts->tv_nsec / UM_NSEC_PER_USEC;
+}
+
+static int after_sleep_interval(struct timespec *ts)
+{
+ int usec = UM_USEC_PER_SEC / UM_HZ;
+ long long start_usecs = timespec_to_us(ts);
+ struct timeval tv;
+ struct itimerval interval;
+
+ /*
+ * It seems that rounding can increase the value returned from
+ * setitimer to larger than the one passed in. Over time,
+ * this will cause the remaining time to be greater than the
+ * tick interval. If this happens, then just reduce the first
+ * tick to the interval value.
+ */
+ if (start_usecs > usec)
+ start_usecs = usec;
+ tv = ((struct timeval) { .tv_sec = start_usecs / UM_USEC_PER_SEC,
+ .tv_usec = start_usecs % UM_USEC_PER_SEC });
+ interval = ((struct itimerval) { { 0, usec }, tv });
+
+ if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
+ return -errno;
+
+ return 0;
+}
+#endif
+
extern void alarm_handler(int sig, struct sigcontext *sc);
void idle_sleep(unsigned long long nsecs)
{
- struct timespec ts = { .tv_sec = nsecs / UM_NSEC_PER_SEC,
- .tv_nsec = nsecs % UM_NSEC_PER_SEC };
+ struct timespec ts;
+
+ /*
+ * nsecs can come in as zero, in which case, this starts a
+ * busy loop. To prevent this, reset nsecs to the tick
+ * interval if it is zero.
+ */
+ if (nsecs == 0)
+ nsecs = UM_NSEC_PER_SEC / UM_HZ;
+ ts = ((struct timespec) { .tv_sec = nsecs / UM_NSEC_PER_SEC,
+ .tv_nsec = nsecs % UM_NSEC_PER_SEC });
if (nanosleep(&ts, &ts) == 0)
alarm_handler(SIGVTALRM, NULL);
+ after_sleep_interval(&ts);
}
-
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