linux-kernel - Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

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Date:   Wed, 12 Jul 2017 20:10:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <fweisbec@...il.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Aubrey Li <aubrey.li@...el.com>, tglx@...utronix.de,
        len.brown@...el.com, rjw@...ysocki.net, tim.c.chen@...ux.intel.com,
        arjan@...ux.intel.com, paulmck@...ux.vnet.ibm.com,
        yang.zhang.wz@...il.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

On Tue, Jul 11, 2017 at 06:09:27PM +0200, Frederic Weisbecker wrote:

> So I'd rather put that on can_stop_idle_tick().

That function needs a fix.. That's not in fact an identity (although it
turns out it is for the 4 default HZ values).

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index c7a899c5ce64..91433bc4a723 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -882,7 +882,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
 	}
 
 	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
-		ts->sleep_length = NSEC_PER_SEC / HZ;
+		ts->sleep_length = TICK_NSEC;
 		return false;
 	}