Hello,
On Monday, October 1, 2007 at 17:38:23 +0200, Alain Guibert wrote:
> We can also try to make adjtimex less sensible to system load. The
> first step on this path [is commited into 1.23]
Now a small second step: The first timestamp in a serie is less accurate
than the following ones. The attached training-gettimeofday.patch
workarounds this by sampling and discarding a first dummy timestamp. The
benefit on accuracy is very variable depending on the machine: 20 µs on
my slow test machine, maybe less on a fast modern PC, probably upto
200 µs on some SoCs (unconfirmed).
> This also reduced a little bit the variability of measures. And
> marginaly reduced the sensibility to system load. It's only a first
> step, though.
The same stands for the second step! ;-)
> BTW I suspect that in cmos_read_time() the case where we are using
> /dev/rtc but ioctl(RTC_UIE_ON) fails, just can't work: It will block
> forever in read() later. Can't verify for sure, because on my machines
> the ioctl(RTC_UIE_ON) succeeds.
This is fixed since adjtimex 1.24, see bug #460065
Alain.
2008-07-28 Alain Guibert <[EMAIL PROTECTED]>
* adjtimex.c (compare, log_times): The first call to
gettimeofday() in a process takes longer than usual, and the
timestamp taken is a little bit late (up to 200 microseconds).
Let's consume this bad call, so that the important timestamps
are all coherant at the top of accuracy.
* (log_times): We don't need the kernel's internal timezone.
Let's stop requesting it.
Signed-off-by: Alain Guibert <[EMAIL PROTECTED]>
diff -prud adjtimex-1.24.orig/adjtimex.c adjtimex-1.24/adjtimex.c
--- adjtimex-1.24.orig/adjtimex.c Mon Jul 28 08:47:56 2008
+++ adjtimex-1.24/adjtimex.c Mon Jul 28 09:42:58 2008
@@ -917,6 +917,10 @@ compare()
int wrote_to_log = 0;
int hz, tick_min, tick_mid, tick_max;
long maxfreq;
+ struct timeval tv_dummy;
+
+ /* dummy training call: the next important timestamp will be more accurate */
+ gettimeofday(&tv_dummy, NULL);
probe_time(&hz, &tick_min, &tick_mid, &tick_max, &maxfreq);
@@ -1104,17 +1108,19 @@ static void log_times()
char ch, buf[64], *s;
int n, ret;
struct timeval tv_sys;
- struct timezone tz;
struct tm bdt;
time_t when, tref;
double ftime_ref, ftime_sys, ftime_cmos;
+ /* dummy training call: the next important timestamp will be more accurate */
+ gettimeofday(&tv_sys, NULL);
+
if (watch)
{
while(1) {
printf("Please press <enter> when you know the time of day: ");
ch = getchar();
- gettimeofday(&tv_sys, &tz);
+ gettimeofday(&tv_sys, NULL);
when = tv_sys.tv_sec;
bdt = *localtime(&when); /* set default values for most fields */
strftime(buf, sizeof(buf), "%Z", &bdt);
@@ -1219,7 +1225,7 @@ offset -0.013543
failntpdate("cannot understand ntpdate output");
ntpdate_okay:
- gettimeofday(&tv_sys, &tz);
+ gettimeofday(&tv_sys, NULL);
ftime_sys = tv_sys.tv_sec;
/* ntpdate selects the offset from one of its samples
(the one with the shortest round-trip delay?) */
@@ -1264,7 +1270,7 @@ offset -0.013543
else /* no absolute time reference */
{
time_t now;
- gettimeofday(&tv_sys, &tz);
+ gettimeofday(&tv_sys, NULL);
now = (time_t)tv_sys.tv_sec;
bdt = *gmtime(&now);
ftime_sys = tv_sys.tv_sec + tv_sys.tv_usec*.000001;
