timers: Optimize _next_timer_interrupt() level iteration (001ec1b3) · Commits · 戴 / test

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:

Frederic Weisbecker <frederic@kernel.org> Signed-off-by:

Thomas Gleixner <tglx@linutronix.de> Tested-by:

Juri Lelli <juri.lelli@redhat.com> Link: https://lkml.kernel.org/r/20200717140551.29076-7-frederic@kernel.org

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;
		}

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