Commit 001ec1b3 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Thomas Gleixner
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timers: Optimize _next_timer_interrupt() level iteration 



If a level has a timer that expires before reaching the next level, there
is no need to iterate further.

The next level is reached when the 3 lower bits of the current level are
cleared. If the next event happens before/during that, the next levels
won't provide an earlier expiration.

Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200717140551.29076-7-frederic@kernel.org
parent 44688972

kernel/time/timer.c

+9 −1
Original line number Diff line number Diff line
@@ -1526,6 +1526,7 @@ static unsigned long __next_timer_interrupt(struct timer_base *base) 
	clk = base->clk;

	for (lvl = 0; lvl < LVL_DEPTH; lvl++, offset += LVL_SIZE) {

		int pos = next_pending_bucket(base, offset, clk & LVL_MASK);

		unsigned long lvl_clk = clk & LVL_CLK_MASK;



		if (pos >= 0) {

			unsigned long tmp = clk + (unsigned long) pos;
@@ -1533,6 +1534,13 @@ static unsigned long __next_timer_interrupt(struct timer_base *base) 
			tmp <<= LVL_SHIFT(lvl);

			if (time_before(tmp, next))

				next = tmp;



			/*

			 * If the next expiration happens before we reach

			 * the next level, no need to check further.

			 */

			if (pos <= ((LVL_CLK_DIV - lvl_clk) & LVL_CLK_MASK))

				break;

		}

		/*

		 * Clock for the next level. If the current level clock lower
@@ -1570,7 +1578,7 @@ static unsigned long __next_timer_interrupt(struct timer_base *base) 
		 * So the simple check whether the lower bits of the current

		 * level are 0 or not is sufficient for all cases.

		 */

		adj = clk & LVL_CLK_MASK ? 1 : 0;

		adj = lvl_clk ? 1 : 0;

		clk >>= LVL_CLK_SHIFT;

		clk += adj;

	}