linux-kernel - Re: Re: [PATCH v1 2/3] arm64: idle: Cache AMU counters before entering idle

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Date: Tue, 12 Mar 2024 09:44:52 +0100
From: Beata Michalska <beata.michalska@....com>
To: Vanshidhar Konda <vanshikonda@...amperecomputing.com>
Cc: "lihuisong (C)" <lihuisong@...wei.com>,
	Ionela Voinescu <ionela.voinescu@....com>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, rafael@...nel.org,
	sumitg@...dia.com, zengheng4@...wei.com,
	yang@...amperecomputing.com, will@...nel.org, sudeep.holla@....com,
	liuyonglong@...wei.com, zhanjie9@...ilicon.com,
	linux-acpi@...r.kernel.org
Subject: Re: Re: [PATCH v1 2/3] arm64: idle: Cache AMU counters before
 entering idle

On Mon, Mar 11, 2024 at 11:27:27AM -0700, Vanshidhar Konda wrote:
> On Thu, Mar 07, 2024 at 11:17:26AM +0800, lihuisong (C) wrote:
> > 
> > 在 2024/3/1 0:25, Vanshidhar Konda 写道:
> > > AMU counters do not increment while a CPU is in idle. Saving the value
> > > of the core and constant counters prior to invoking WFI allows FIE to
> > > compute the frequency of a CPU that is idle.
> > > 
> > > Signed-off-by: Vanshidhar Konda <vanshikonda@...amperecomputing.com>
> > > ---
> > >  arch/arm64/kernel/idle.c     | 10 ++++++++++
> > >  arch/arm64/kernel/topology.c | 14 ++++++++------
> > >  2 files changed, 18 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/arch/arm64/kernel/idle.c b/arch/arm64/kernel/idle.c
> > > index 05cfb347ec26..5ed2e57188a8 100644
> > > --- a/arch/arm64/kernel/idle.c
> > > +++ b/arch/arm64/kernel/idle.c
> > > @@ -26,6 +26,16 @@ void __cpuidle cpu_do_idle(void)
> > >  	arm_cpuidle_save_irq_context(&context);
> > > +#ifdef CONFIG_ARM64_AMU_EXTN
> > > +	/* Update the AMU counters before entering WFI. The cached AMU counter
> > > +	 * value is used to determine CPU frequency while the CPU is idle
> > > +	 * without needing to wake up the CPU.
> > > +	 */
> > > +
> > > +	if (cpu_has_amu_feat(smp_processor_id()))
> > > +		update_freq_counters_refs();
> > > +#endif
> > The below point I has mentioned in [1].
> > This is just for the WFI state.
> > What about other deeper idle states, like retention and power down?
> > The path to enter idle state is different for them. We should do this
> > for all idle states.
> > 
> 
> Yes. That makes sense. I'll account for them in the next version of the
> patch. I'll work on the next version of the patch based on the updated
> patch from @Beata.
> 
This should now be covered by [1]

---
[1]https://lore.kernel.org/all/20240312083431.3239989-4-beata.michalska@arm.com/

---
BR
Beata

> Thanks,
> Vanshi
> 
> > > +
> > >  	dsb(sy);
> > >  	wfi();
> > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> > > index db8d14525cf4..8905eb0c681f 100644
> > > --- a/arch/arm64/kernel/topology.c
> > > +++ b/arch/arm64/kernel/topology.c
> > > @@ -240,13 +240,15 @@ unsigned int arch_freq_get_on_cpu(int cpu)
> > >  	} while (read_seqcount_retry(&cpu_sample->seq, seq));
> > >  	/*
> > > -	 * Bail on invalid count and when the last update was too long ago,
> > > -	 * which covers idle and NOHZ full CPUs.
> > > +	 * Bail on invalid count and when the last update was too long ago.
> > > +	 * This covers idle, NOHZ full and isolated CPUs.
> > > +	 *
> > > +	 * Idle CPUs don't need to be measured because AMU counters stop
> > > +	 * incrementing during WFI/WFE.
> > >  	 */
> > > -	if (!delta_const_cnt || ((jiffies - last) > MAX_SAMPLE_AGE)) {
> > > -		if (!(housekeeping_cpu(cpu, HK_TYPE_TICK) && idle_cpu(cpu)))
> > > -			goto fallback;
> > > -	}
> > > +	if (!delta_const_cnt ||
> > > +	    ((jiffies - last) > MAX_SAMPLE_AGE && !idle_cpu(cpu)))
> > > +		goto fallback;
> > >  	/*
> > >  	 * CPU frequency = reference perf (in Hz) * (/\ delivered) / (/\ reference)
> > [1] https://lore.kernel.org/linux-arm-kernel/20231212072617.14756-1-lihuisong@huawei.com/
> >