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SubjectRe: [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@suse.cz>
> > AuthorDate: Wed, 22 Jan 2020 16:16:12 +01:00
> > Committer: Ingo Molnar <mingo@kernel.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();

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