On 06/22/12 10:06, Konstantin Belousov wrote:
Author: kib
Date: Fri Jun 22 07:06:40 2012
New Revision: 237433
URL: http://svn.freebsd.org/changeset/base/237433
Log:
Implement mechanism to export some kernel timekeeping data to
usermode, using shared page. The structures and functions have vdso
prefix, to indicate the intended location of the code in some future.
The versioned per-algorithm data is exported in the format of struct
vdso_timehands, which mostly repeats the content of in-kernel struct
timehands. Usermode reading of the structure can be lockless.
Compatibility export for 32bit processes on 64bit host is also
provided. Kernel also provides usermode with indication about
currently used timecounter, so that libc can fall back to syscall if
configured timecounter is unknown to usermode code.
The shared data updates are initiated both from the tc_windup(), where
a fast task is queued to do the update, and from sysctl handlers which
change timecounter. A manual override switch
kern.timecounter.fast_gettime allows to turn off the mechanism.
Only x86 architectures export the real algorithm data, and there, only
for tsc timecounter. HPET counters page could be exported as well, but
I prefer to not further glue the kernel and libc ABI there until
proper vdso-based solution is developed.
Minimal stubs neccessary for non-x86 architectures to still compile
are provided.
Discussed with: bde
Reviewed by: jhb
Tested by: flo
MFC after: 1 month
@@ -1360,6 +1367,7 @@ tc_windup(void)
#endif
timehands = th;
+ taskqueue_enqueue_fast(taskqueue_fast,&tc_windup_push_vdso_task);
}
/* Report or change the active timecounter hardware. */
This taskqueue_enqueue_fast() will schedule extra thread to run each
time hardclock() fires. One thread may be not a big problem, but
together with callout swi and possible other threads woken up there it
will wake up several other CPU cores from sleep just to put them back in
few microseconds. Now davide@ and me are trying to fix that by avoiding
callout SWI use for simple tasks. Please, let's not create another
problem same time.
--
Alexander Motin
_______________________________________________
svn-src-head@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/svn-src-head
To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
