john stultz wrote:
> I believe you're right. Although we don't call read_persistent_clock()
> very frequently, nor do we call it in ways we don't already call
> get_cmos_time(). So I'm not sure exactly what the concern is.
Sorry - I should have given more context. I am worried about
suspend and resume times. An extra (up-to-a) second delay on
suspend it pretty painful for CE devices. (See my SIG for
my other hat in the forum.)
>
> Since we call read_persistent_clock(), it should return right as the
> second changes, thus we will be marking the new second as closely as
> possible with the timesource value. If the order was reversed, I think
> it would be a concern.
>
It sounds like for your code, this synchronization is a valuable.
For many CE products, the synchronization is not needed. I have a
patch that removes the synchronization for i386 and ppc, but
I haven't submitted it because I didn't want to mess up
non-boot-context callers of get_cmos_time which have valid
synchronization needs.
As you can see below, the patch is pretty braindead.
I was wondering if this conflicted with your new timer system or
not.
diffstat:
arch/ppc/kernel/time.c | 10 ++++++++--
include/asm-i386/mach-default/mach_time.h | 6 +++++-
init/Kconfig | 27 +++++++++++++++++++++++++++
3 files changed, 40 insertions(+), 3 deletions(-)
Signed-off-by: Tim Bird <[EMAIL PROTECTED]>
-----------------------
diff -pruN -X /home/tbird/dontdiff linux-2.6.10.orig/arch/ppc/kernel/time.c
linux-2.6.10/arch/ppc/kernel/time.c
--- linux-2.6.10.orig/arch/ppc/kernel/time.c 2004-12-24 13:35:23.000000000
-0800
+++ linux-2.6.10/arch/ppc/kernel/time.c 2005-02-01 15:28:42.539108108 -0800
@@ -291,8 +291,12 @@ EXPORT_SYMBOL(do_settimeofday);
/* This function is only called on the boot processor */
void __init time_init(void)
{
- time_t sec, old_sec;
- unsigned old_stamp, stamp, elapsed;
+ time_t sec;
+ unsigned stamp;
+#ifndef CONFIG_RTC_NO_SYNC
+ time_t old_sec;
+ unsigned old_stamp, elapsed;
+#endif
if (ppc_md.time_init != NULL)
time_offset = ppc_md.time_init();
@@ -317,6 +321,7 @@ void __init time_init(void)
stamp = get_native_tbl();
if (ppc_md.get_rtc_time) {
sec = ppc_md.get_rtc_time();
+#ifndef CONFIG_RTC_NO_SYNC
elapsed = 0;
do {
old_stamp = stamp;
@@ -329,6 +334,7 @@ void __init time_init(void)
} while ( sec == old_sec && elapsed < 2*HZ*tb_ticks_per_jiffy);
if (sec==old_sec)
printk("Warning: real time clock seems stuck!\n");
+#endif
xtime.tv_sec = sec;
xtime.tv_nsec = 0;
/* No update now, we just read the time from the RTC ! */
diff -pruN -X /home/tbird/dontdiff
linux-2.6.10.orig/include/asm-i386/mach-default/mach_time.h
linux-2.6.10/include/asm-i386/mach-default/mach_time.h
--- linux-2.6.10.orig/include/asm-i386/mach-default/mach_time.h 2004-12-24
13:34:30.000000000 -0800
+++ linux-2.6.10/include/asm-i386/mach-default/mach_time.h 2005-02-01
15:28:48.245009070 -0800
@@ -89,6 +89,7 @@ static inline unsigned long mach_get_cmo
* RTC registers show the second which has precisely just started.
* Let's hope other operating systems interpret the RTC the same way.
*/
+#ifndef CONFIG_RTC_NO_SYNC_ON_READ
/* read RTC exactly on falling edge of update flag */
for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
@@ -96,7 +97,10 @@ static inline unsigned long mach_get_cmo
for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
break;
- do { /* Isn't this overkill ? UIP above should guarantee consistency */
+/* The following is probably overkill because
+ * UIP above should guarantee consistency */
+#endif
+ do {
sec = CMOS_READ(RTC_SECONDS);
min = CMOS_READ(RTC_MINUTES);
hour = CMOS_READ(RTC_HOURS);
diff -pruN -X /home/tbird/dontdiff linux-2.6.10.orig/init/Kconfig
linux-2.6.10/init/Kconfig
--- linux-2.6.10.orig/init/Kconfig 2004-12-24 13:35:24.000000000 -0800
+++ linux-2.6.10/init/Kconfig 2005-02-01 15:28:48.281002137 -0800
@@ -248,6 +248,33 @@ config IKCONFIG_PROC
This option enables access to the kernel configuration file
through /proc/config.gz.
+menuconfig FASTBOOT
+ bool "Fast boot options"
+ help
+ Say Y here to select among various options that can decrease
+ kernel boot time. These options may involve providing
+ hardcoded values for some parameters that the kernel usually
+ determines automatically.
+
+ This option is useful primarily on embedded systems.
+
+ If unsure, say N.
+
+config RTC_NO_SYNC
+ bool "Disable synch on read of Real Time Clock" if FASTBOOT
+ default n
+ help
+ The Real Time Clock is read aligned by default. That means a
+ series of reads of the RTC are done until it's verified that
+ the RTC's state has just changed. If you enable this feature,
+ this synchronization will not be performed. The result is that
+ the machine will boot up to 1 second faster.
+
+ A drawback is that, with this option enabled, your system
+ clock may drift from the correct value over the course
+ of several boot cycles (under certain circumstances).
+
+ If unsure, say N.
menuconfig EMBEDDED
bool "Configure standard kernel features (for small systems)"
-
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