Re: struct timehands: th_generation field
OK. I read the document and understood it I guess. Very interesting, and well engineered. On x86/i386/amd64, could not all this be replaced by a simple call to apic timer ? We would get the timestamp, we can even store it, make calculation on top of it. My jugement may miss something important though. That is why I ask :) -- Jog ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: struct timehands: th_generation field
accessing hardware isn't free. Locking also isn't free. That's why there's this mechanism. -adrian On 24 July 2015 at 08:58, deco33...@yandex.com wrote: OK. I read the document and understood it I guess. Very interesting, and well engineered. On x86/i386/amd64, could not all this be replaced by a simple call to apic timer ? We would get the timestamp, we can even store it, make calculation on top of it. My jugement may miss something important though. That is why I ask :) -- Jog ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: struct timehands: th_generation field
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Re: struct timehands: th_generation field
On Thu, Jul 23, 2015 at 9:43 AM, deco33...@yandex.com wrote:
I am struggling on one field of a struct :
http://fxr.watson.org/fxr/source/kern/kern_tc.c?v=FREEBSD10#L63
I would like to understand what th_generation means please.
Seems to me you get a clue from: (
http://fxr.watson.org/fxr/source/kern/kern_tc.c?v=FREEBSD10#L192)
*/*** * Functions for reading the time. We have to loop until we are
sure that** * the timehands that we operated on was not updated under
our feet. See** * the comment in sys/time.h for a description of
these 12 functions.** */*
#ifdef FFCLOCK
voidfbclock_binuptime
http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=fbclock_binuptime(struct
bintime http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=bintime *bt
http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=bt)
{
struct timehands
http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=timehands *th;
unsigned int gen http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=gen;
do {
th = timehands
http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=timehands;
gen http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=gen =
th-th_generation;
*bt http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=bt =
th-th_offset;
bintime_addx
http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=bintime_addx(bt
http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=bt, th-th_scale * tc_delta
http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=tc_delta(th));
} while (gen http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=gen == 0
|| gen http://fxr.watson.org/fxr/ident?v=FREEBSD10;i=gen !=
th-th_generation);
}
--
brandon s allbery kf8nh sine nomine associates
allber...@gmail.com ballb...@sinenomine.net
unix, openafs, kerberos, infrastructure, xmonadhttp://sinenomine.net
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struct timehands: th_generation field
Hi, Currently I read more about timers and clock. I am struggling on one field of a struct : http://fxr.watson.org/fxr/source/kern/kern_tc.c?v=FREEBSD10#L63 I would like to understand what th_generation means please. Thanks a lot -- Jog ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: struct timehands: th_generation field
On Thu, Jul 23, 2015 at 10:38 AM, deco33...@yandex.com wrote: Is the maximum value for th_generation equal to 10 ? http://fxr.watson.org/fxr/source/kern/kern_tc.c?v=FREEBSD10#L77 I don't think those relate to generations. Generations change on every clock tick; the multiple timehands structs relate to forcibly setting the time, as opposed to the clock moving forward normally. It does appear serve a similar purpose, since forcibly setting the time is even more violent (to anything currently reading the clock) than advancing the clock on a clock tick, since that's when other adjustments including possibly switching the clock source will be applied. -- brandon s allbery kf8nh sine nomine associates allber...@gmail.com ballb...@sinenomine.net unix, openafs, kerberos, infrastructure, xmonadhttp://sinenomine.net ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
Re: struct timehands: th_generation field
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Re: struct timehands: th_generation field
On Thu, 2015-07-23 at 10:59 -0400, Brandon Allbery wrote: On Thu, Jul 23, 2015 at 10:38 AM, deco33...@yandex.com wrote: Is the maximum value for th_generation equal to 10 ? http://fxr.watson.org/fxr/source/kern/kern_tc.c?v=FREEBSD10#L77 I don't think those relate to generations. Generations change on every clock tick; the multiple timehands structs relate to forcibly setting the time, as opposed to the clock moving forward normally. It does appear serve a similar purpose, since forcibly setting the time is even more violent (to anything currently reading the clock) than advancing the clock on a clock tick, since that's when other adjustments including possibly switching the clock source will be applied. Ummm, no. The multiple timehands and related generation count are all about time moving forward normally, and doing so without needing mutxes or other locking primitives to obtain the current time. I think you guys need to read this... http://phk.freebsd.dk/pubs/timecounter.pdf Especially the section named Locking, lack of... -- Ian ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to freebsd-stable-unsubscr...@freebsd.org
