Messages in this thread Patch in this message | | | Date | Fri, 03 Mar 2006 11:44:06 +0900 (JST) | Subject | Re: [PATCH] simplify update_times (avoid jiffies/jiffies_64 aliasing problem) | From | Atsushi Nemoto <> |
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>>>>> On Thu, 2 Mar 2006 11:09:16 -0800 (PST), Christoph Lameter <clameter@engr.sgi.com> said: >> In kernel 2.6, update_times() is called directly in timer >> interrupt, so there is no point calculating ticks here. This also >> get rid of difference of jiffies and jiffies_64 due to compiler's >> optimization (which was reported previously with subject >> "jiffies_64 vs. jiffies").
clameter> If update_wall_time() and calc_load() are always called with clameter> the constant one then you may be able to optimize these two clameter> functions as well.
Sure. I tried to do only one thing at a time, but it might be better to clean them up together. Patch revised.
In kernel 2.6, update_times() is called directly in timer interrupt, so there is no point calculating ticks here. Then update_wall_time() and calc_load() can also be optimized. This also get rid of difference of jiffies and jiffies_64 due to compiler's optimization (which was reported previously with subject "jiffies_64 vs. jiffies").
Also adjust x86_64 timer interrupt handler with this change.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c index 3080f84..7a1d790 100644 --- a/arch/x86_64/kernel/time.c +++ b/arch/x86_64/kernel/time.c @@ -423,7 +423,8 @@ void main_timer_handler(struct pt_regs * if (lost > 0) { handle_lost_ticks(lost, regs); - jiffies += lost; + while (lost--) + do_timer(regs); } /* diff --git a/kernel/timer.c b/kernel/timer.c index fc6646f..54544a7 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -787,24 +787,14 @@ u64 current_tick_length(void) return ((u64) delta_nsec << (SHIFT_SCALE - 10)) + time_adj; } -/* - * Using a loop looks inefficient, but "ticks" is - * usually just one (we shouldn't be losing ticks, - * we're doing this this way mainly for interrupt - * latency reasons, not because we think we'll - * have lots of lost timer ticks - */ -static void update_wall_time(unsigned long ticks) +static void update_wall_time(void) { - do { - ticks--; - update_wall_time_one_tick(); - if (xtime.tv_nsec >= 1000000000) { - xtime.tv_nsec -= 1000000000; - xtime.tv_sec++; - second_overflow(); - } - } while (ticks); + update_wall_time_one_tick(); + if (xtime.tv_nsec >= 1000000000) { + xtime.tv_nsec -= 1000000000; + xtime.tv_sec++; + second_overflow(); + } } /* @@ -849,15 +839,15 @@ unsigned long avenrun[3]; EXPORT_SYMBOL(avenrun); /* - * calc_load - given tick count, update the avenrun load estimates. + * calc_load - update the avenrun load estimates. * This is called while holding a write_lock on xtime_lock. */ -static inline void calc_load(unsigned long ticks) +static inline void calc_load(void) { unsigned long active_tasks; /* fixed-point */ static int count = LOAD_FREQ; - count -= ticks; + count--; if (count < 0) { count += LOAD_FREQ; active_tasks = count_active_tasks(); @@ -906,14 +896,9 @@ void run_local_timers(void) */ static inline void update_times(void) { - unsigned long ticks; - - ticks = jiffies - wall_jiffies; - if (ticks) { - wall_jiffies += ticks; - update_wall_time(ticks); - } - calc_load(ticks); + wall_jiffies++; + update_wall_time(); + calc_load(); } /* - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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