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Date: Thu, 02 Jul 2020 17:14:23 +0200 From: Thomas Gleixner <tglx@...utronix.de> To: Frederic Weisbecker <frederic@...nel.org> Cc: LKML <linux-kernel@...r.kernel.org>, Anna-Maria Gleixner <anna-maria@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com> Subject: Re: [RFC PATCH 10/10] timer: Lower base clock forwarding threshold Frederic Weisbecker <frederic@...nel.org> writes: > On Thu, Jul 02, 2020 at 03:21:35PM +0200, Thomas Gleixner wrote: >> Frederic Weisbecker <frederic@...nel.org> writes: >> > @@ -883,7 +883,7 @@ static inline void forward_timer_base(struct timer_base *base) >> > * Also while executing timers, base->clk is 1 offset ahead >> > * of jiffies to avoid endless requeuing to current jffies. >> > */ >> > - if ((long)(jnow - base->clk) < 2) >> > + if ((long)(jnow - base->clk) < 1) >> > return; >> >> The apparent reason is in the comment right above the condition ... > > Hmm, that's a comment I added myself in the patch before. :) > The following part: > >> > * Also while executing timers, base->clk is 1 offset ahead >> > * of jiffies to avoid endless requeuing to current jffies. >> > */ > > relates to situation when (long)(jnow - base->clk) < 0 This still is inconsistent with your changelog: > There is no apparent reason for not forwarding base->clk when it's 2 > jiffies late Let's do the math: jiffies = 4 base->clk = 2 4 - 2 = 2 which means it is forwarded when it's 2 jiffies late with the original code, because 2 < 2. The reason for this < 2 is historical and goes back to the oddities of the original timer wheel before the big rewrite. Thanks, tglx
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