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authorWoodruff, Richard <r-woodruff2@ti.com>2008-12-01 17:18:11 -0500
committerThomas Gleixner <tglx@linutronix.de>2008-12-12 10:55:31 -0500
commit001474491fabeca233168a8598f721c808040f90 (patch)
tree858467ce6aed38ba2bd1ea8682e12bbdb182d0f1 /kernel/time/tick-sched.c
parentfa116ea35ec7f40e890972324409e99eed008d56 (diff)
nohz: suppress needless timer reprogramming
In my device I get many interrupts from a high speed USB device in a very short period of time. The system spends a lot of time reprogramming the hardware timer which is in a slower timing domain as compared to the CPU. This results in the CPU spending a huge amount of time waiting for the timer posting to be done. All of this reprogramming is useless as the wake up time has not changed. As measured using ETM trace this drops my reprogramming penalty from almost 60% CPU load down to 15% during high interrupt rate. I can send traces to show this. Suppress setting of duplicate timer event when timer already stopped. Timer programming can be very costly and can result in long cpu stall/wait times. [akpm@linux-foundation.org: coding-style fixes] [tglx@linutronix.de: move the check to the right place and avoid raising the softirq for nothing] Signed-off-by: Richard Woodruff <r-woodruff2@ti.com> Cc: johnstul@us.ibm.com Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/time/tick-sched.c')
-rw-r--r--kernel/time/tick-sched.c41
1 files changed, 24 insertions, 17 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index dc17ffcf1919..87fc34f21db2 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -282,8 +282,31 @@ void tick_nohz_stop_sched_tick(int inidle)
282 /* Schedule the tick, if we are at least one jiffie off */ 282 /* Schedule the tick, if we are at least one jiffie off */
283 if ((long)delta_jiffies >= 1) { 283 if ((long)delta_jiffies >= 1) {
284 284
285 /*
286 * calculate the expiry time for the next timer wheel
287 * timer
288 */
289 expires = ktime_add_ns(last_update, tick_period.tv64 *
290 delta_jiffies);
291
292 /*
293 * If this cpu is the one which updates jiffies, then
294 * give up the assignment and let it be taken by the
295 * cpu which runs the tick timer next, which might be
296 * this cpu as well. If we don't drop this here the
297 * jiffies might be stale and do_timer() never
298 * invoked.
299 */
300 if (cpu == tick_do_timer_cpu)
301 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
302
285 if (delta_jiffies > 1) 303 if (delta_jiffies > 1)
286 cpu_set(cpu, nohz_cpu_mask); 304 cpu_set(cpu, nohz_cpu_mask);
305
306 /* Skip reprogram of event if its not changed */
307 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
308 goto out;
309
287 /* 310 /*
288 * nohz_stop_sched_tick can be called several times before 311 * nohz_stop_sched_tick can be called several times before
289 * the nohz_restart_sched_tick is called. This happens when 312 * the nohz_restart_sched_tick is called. This happens when
@@ -306,17 +329,6 @@ void tick_nohz_stop_sched_tick(int inidle)
306 rcu_enter_nohz(); 329 rcu_enter_nohz();
307 } 330 }
308 331
309 /*
310 * If this cpu is the one which updates jiffies, then
311 * give up the assignment and let it be taken by the
312 * cpu which runs the tick timer next, which might be
313 * this cpu as well. If we don't drop this here the
314 * jiffies might be stale and do_timer() never
315 * invoked.
316 */
317 if (cpu == tick_do_timer_cpu)
318 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
319
320 ts->idle_sleeps++; 332 ts->idle_sleeps++;
321 333
322 /* 334 /*
@@ -332,12 +344,7 @@ void tick_nohz_stop_sched_tick(int inidle)
332 goto out; 344 goto out;
333 } 345 }
334 346
335 /* 347 /* Mark expiries */
336 * calculate the expiry time for the next timer wheel
337 * timer
338 */
339 expires = ktime_add_ns(last_update, tick_period.tv64 *
340 delta_jiffies);
341 ts->idle_expires = expires; 348 ts->idle_expires = expires;
342 349
343 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 350 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {