lkml.org 
[lkml]   [2008]   [Mar]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [2.6.24.x] UML select()/poll() oversleeping reproducibly
Below is another patch.

I was hurt and disappointed by your
> Eeuuuuw. :)
so I got rid of the 9/10 thing.

This version keeps track of the time between ticks (as reported by the
host's gettimeofday) and adjusts its sleeping and reporting ticks
accordingly.

It's still undersleeping a little - your little test once reported 19
seconds for a 20 second sleep. Otherwise, it's reporting sleep times
that are right on the money.

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 2008-03-18 12:32:19.000000000 -0400
+++ linux-2.6.22/arch/um/os-Linux/time.c 2008-03-18 12:45:50.000000000 -0400
@@ -11,6 +11,7 @@
#include "kern_constants.h"
#include "os.h"
#include "user.h"
+#include "kern_util.h"

int set_interval(void)
{
@@ -58,12 +59,17 @@ static inline long long timeval_to_ns(co
long long disable_timer(void)
{
struct itimerval time = ((struct itimerval) { { 0, 0 }, { 0, 0 } });
+ int remain, max = UM_NSEC_PER_SEC / UM_HZ;

if (setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
printk(UM_KERN_ERR "disable_timer - setitimer failed, "
"errno = %d\n", errno);

- return timeval_to_ns(&time.it_value);
+ remain = timeval_to_ns(&time.it_value);
+ if (remain > max)
+ remain = max;
+
+ return remain;
}

long long os_nsecs(void)
@@ -79,7 +85,47 @@ static int after_sleep_interval(struct t
{
return 0;
}
+
+
+static void deliver_alarm(void)
+{
+ alarm_handler(SIGVTALRM, NULL);
+}
+
+static unsigned long long sleep_time(unsigned long long nsecs)
+{
+ return nsecs;
+}
+
#else
+unsigned long long last_tick;
+unsigned long long skew;
+
+extern void alarm_handler(int sig, struct sigcontext *sc);
+
+static void deliver_alarm(void)
+{
+ unsigned long long this_tick = os_nsecs();
+ int one_tick = UM_NSEC_PER_SEC / UM_HZ;
+
+ if (last_tick == 0)
+ last_tick = this_tick - one_tick;
+
+ skew += this_tick - last_tick;
+
+ while (skew >= one_tick) {
+ alarm_handler(SIGVTALRM, NULL);
+ skew -= one_tick;
+ }
+
+ last_tick = this_tick;
+}
+
+static unsigned long long sleep_time(unsigned long long nsecs)
+{
+ return nsecs > skew ? nsecs - skew : 0;
+}
+
static inline long long timespec_to_us(const struct timespec *ts)
{
return ((long long) ts->tv_sec * UM_USEC_PER_SEC) +
@@ -102,6 +148,8 @@ static int after_sleep_interval(struct t
*/
if (start_usecs > usec)
start_usecs = usec;
+
+ start_usecs -= skew / UM_NSEC_PER_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 });
@@ -113,8 +161,6 @@ static int after_sleep_interval(struct t
}
#endif

-extern void alarm_handler(int sig, struct sigcontext *sc);
-
void idle_sleep(unsigned long long nsecs)
{
struct timespec ts;
@@ -126,10 +172,12 @@ void idle_sleep(unsigned long long nsecs
*/
if (nsecs == 0)
nsecs = UM_NSEC_PER_SEC / UM_HZ;
+
+ nsecs = sleep_time(nsecs);
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);
+ deliver_alarm();
after_sleep_interval(&ts);
}

\
 
 \ /
  Last update: 2008-03-19 22:13    [W:0.054 / U:0.824 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site