linux-kernel - Re: [tip: sched/core] x86, sched: Add support for frequency invariance

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Date:   Mon, 30 Mar 2020 14:52:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chris Wilson <chris@...is-wilson.co.uk>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        tip-bot2 for Giovanni Gherdovich <tip-bot2@...utronix.de>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Ingo Molnar <mingo@...nel.org>,
        Doug Smythies <dsmythies@...us.net>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        x86 <x86@...nel.org>
Subject: Re: [tip: sched/core] x86, sched: Add support for frequency
 invariance

On Mon, Mar 30, 2020 at 12:05:42PM +0100, Chris Wilson wrote:
> Quoting tip-bot2 for Giovanni Gherdovich (2020-01-29 11:32:58)
> > The following commit has been merged into the sched/core branch of tip:
> > 
> > Commit-ID:     1567c3e3467cddeb019a7b53ec632f834b6a9239
> > Gitweb:        https://git.kernel.org/tip/1567c3e3467cddeb019a7b53ec632f834b6a9239
> > Author:        Giovanni Gherdovich <ggherdovich@...e.cz>
> > AuthorDate:    Wed, 22 Jan 2020 16:16:12 +01:00
> > Committer:     Ingo Molnar <mingo@...nel.org>
> > CommitterDate: Tue, 28 Jan 2020 21:36:59 +01:00
> > 
> > x86, sched: Add support for frequency invariance
> > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> > index 69881b2..28696bc 100644
> > --- a/arch/x86/kernel/smpboot.c
> > +++ b/arch/x86/kernel/smpboot.c
> > @@ -147,6 +147,8 @@ static inline void smpboot_restore_warm_reset_vector(void)
> >         *((volatile u32 *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = 0;
> >  }
> >  
> > +static void init_freq_invariance(void);
> > +
> >  /*
> >   * Report back to the Boot Processor during boot time or to the caller processor
> >   * during CPU online.
> > @@ -183,6 +185,8 @@ static void smp_callin(void)
> >          */
> >         set_cpu_sibling_map(raw_smp_processor_id());
> >  
> > +       init_freq_invariance();
> > +
> >         /*
> >          * Get our bogomips.
> >          * Update loops_per_jiffy in cpu_data. Previous call to
> > @@ -1337,7 +1341,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
> >         set_sched_topology(x86_topology);
> >  
> >         set_cpu_sibling_map(0);
> > -
> > +       init_freq_invariance();
> >         smp_sanity_check();
> >  
> >         switch (apic_intr_mode) {
> 
> Since this has become visible via linux-next [20200326?], we have been
> deluged by oops during cpu-hotplug.

Ooh, you're doing CPU-0 hotplug, yuck!

I think something like the below ought to work; let me go see if I can
get that cpu-0 hotplug crud working on my machines.

---

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index fe3ab9632f3b..681f96f05619 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -147,7 +147,7 @@ static inline void smpboot_restore_warm_reset_vector(void)
 	*((volatile u32 *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = 0;
 }
 
-static void init_freq_invariance(void);
+static void init_freq_invariance(bool secondary);
 
 /*
  * Report back to the Boot Processor during boot time or to the caller processor
@@ -185,7 +185,7 @@ static void smp_callin(void)
 	 */
 	set_cpu_sibling_map(raw_smp_processor_id());
 
-	init_freq_invariance();
+	init_freq_invariance(true);
 
 	/*
 	 * Get our bogomips.
@@ -1341,7 +1341,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 	set_sched_topology(x86_topology);
 
 	set_cpu_sibling_map(0);
-	init_freq_invariance();
+	init_freq_invariance(false);
 	smp_sanity_check();
 
 	switch (apic_intr_mode) {
@@ -2002,13 +2002,20 @@ static void init_counter_refs(void *arg)
 	this_cpu_write(arch_prev_mperf, mperf);
 }
 
-static void init_freq_invariance(void)
+static void init_freq_invariance(bool secondary)
 {
 	bool ret = false;
 
-	if (smp_processor_id() != 0 || !boot_cpu_has(X86_FEATURE_APERFMPERF))
+	if (!boot_cpu_has(X86_FEATURE_APERFMPERF))
 		return;
 
+	if (secondary) {
+		if (static_branch_likely(&arch_scale_freq_key)) {
+			init_counter_refs(NULL);
+		}
+		return;
+	}
+
 	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
 		ret = intel_set_max_freq_ratio();