linux-kernel - Re: [PATCH] arm64: add cpu_idle tracepoints to arch_cpu

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Date:	Thu, 17 Sep 2015 00:56:47 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: add cpu_idle tracepoints to arch_cpu_idle

On Wed, 16 Sep 2015 17:16:05 +0100
Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote:

> On Wed, Sep 16, 2015 at 04:11:05PM +0100, Jisheng Zhang wrote:
> > Dear Lorenzo,
> > 
> > On Wed, 16 Sep 2015 22:53:12 +0800
> > Jisheng Zhang <jszhang@...vell.com> wrote:
> > 
> > > Dear Lorenzo,
> > > 
> > > On Wed, 16 Sep 2015 15:47:38 +0100
> > > Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote:
> > > 
> > > > On Wed, Sep 16, 2015 at 03:23:21PM +0100, Jisheng Zhang wrote:
> > > > > Currently, if cpuidle is disabled or not supported, powertop reports
> > > > > zero wakeups and zero events. This is due to the cpu_idle tracepoints
> > > > > are missing.
> > > > > 
> > > > > This patch is to make cpu_idle tracepoints always available even if
> > > > > cpuidle is disabled or not supported.
> > > > > 
> > > > > Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> > > > 
> > > > Is there a reason why this code cannot be moved to the generic idle loop ?
> > > 
> > > Do you mean the cpu_idle_loop() in kernel/sched/idle.c? To be honest, I
> > 
> > Maybe I know now. we need to trace different idle level, for example:
> > 
> > WFI idle: trace_cpu_idle_rcuidle(1, ...);
> > 
> > deeper idle: trace_cpu_idle_rcuidle(2, ...);
> > 
> > Usually, the first argument of trace_cpu_idle_rcuidle() equals to the index
> > of the idle level.
> > 
> > so generic idle loop is not a good candidate.
> 
> You are adding a trace for tracing state 1 (ie default idle state),
> called from arch_cpu_idle(), which is the default idle call when the
> CPUidle framework is not available, so I suggested moving the traces
> you add to arm/arm64 arch_cpu_idle() calls to kernel/sched/idle.c
> (see default_idle_call()) instead of patching architecture code.
> 
> I think you can't do that because on x86 calling arch_cpu_idle()
> does not always mean entering idle state index 1 if I read the code
> correctly (in particular the mwait based implementation - mwait_idle()).
> 
> So never mind, patch is fine (on arm64, on arm you should be careful
> because some arm_pm_idle implementations trace state 1 already -
> see omap3_pm_idle and if you add traces to arch_cpu_idle you should
> remove the traces from mach implementations).

OOPs, I was debugging the cascaded irq issues on Marvell BG4CT SoC. Yes, this
arm_pm_idle should be taken care on arm, I should ignore arm_pm_idle, I'll
cook v2 for arm platform.

Thanks a lot,
Jisheng

> 
> Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>

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