Re: uml doesn't work on 2.6.24-rc2

Jeff Dike
2007-11-26T20:54:04Z

On Wed, Nov 14, 2007 at 04:26:11PM +0100, Miklos Szeredi wrote:
> This one fixed the EINVAL messages, and now UML boots, but consumes
> 100% CPU constantly.

Can you disable NO_HZ and try the patch below, which WorksForMe (TM)?

Jeff

--
Work email - jdike at linux dot intel dot com

Index: linux-2.6.22/arch/um/os-Linux/time.c
===================================================================
--- linux-2.6.22.orig/arch/um/os-Linux/time.c 2007-11-14 10:33:29.000000000 -0500
+++ linux-2.6.22/arch/um/os-Linux/time.c 2007-11-26 15:50:46.000000000 -0500
@@ -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);
}