| Message ID | 10523497.nUPlyArG6x@rjwysocki.net (mailing list archive) |
|---|---|
| State | In Next |
| Delegated to: | Rafael Wysocki |
| Headers | show |
| Series | x86 / intel_pstate: Set asymmetric CPU capacity on hybrid systems | expand |
On Wed, Aug 28, 2024 at 01:47:25PM +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > In order be able to compute the sizes of tasks consistently across all > CPUs in a hybrid system, it is necessary to provide CPU capacity scaling > information to the scheduler via arch_scale_cpu_capacity(). Moreover, > the value returned by arch_scale_freq_capacity() for the given CPU must > correspond to the arch_scale_cpu_capacity() return value for it, or > utilization computations will be inaccurate. > > Add support for it through per-CPU variables holding the capacity and > maximum-to-base frequency ratio (times SCHED_CAPACITY_SCALE) that will > be returned by arch_scale_cpu_capacity() and used by scale_freq_tick() > to compute arch_freq_scale for the current CPU, respectively. > > In order to avoid adding measurable overhead for non-hybrid x86 systems, > which are the vast majority in the field, whether or not the new hybrid > CPU capacity scaling will be in effect is controlled by a static key. > This static key is set by calling arch_enable_hybrid_capacity_scale() > which also allocates memory for the per-CPU data and initializes it. > Next, arch_set_cpu_capacity() is used to set the per-CPU variables > mentioned above for each CPU and arch_rebuild_sched_domains() needs > to be called for the scheduler to realize that capacity-aware > scheduling can be used going forward. > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Looks about right; would be good to hear from the AMD folks if they can use it as is, but if not, it should be simple enough to fix up later. Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > arch/x86/include/asm/topology.h | 13 +++++ > arch/x86/kernel/cpu/aperfmperf.c | 89 ++++++++++++++++++++++++++++++++++++++- > 2 files changed, 100 insertions(+), 2 deletions(-) > > Index: linux-pm/arch/x86/include/asm/topology.h > =================================================================== > --- linux-pm.orig/arch/x86/include/asm/topology.h > +++ linux-pm/arch/x86/include/asm/topology.h > @@ -282,9 +282,22 @@ static inline long arch_scale_freq_capac > } > #define arch_scale_freq_capacity arch_scale_freq_capacity > > +bool arch_enable_hybrid_capacity_scale(void); > +void arch_set_cpu_capacity(int cpu, unsigned long cap, unsigned long max_cap, > + unsigned long cap_freq, unsigned long base_freq); > + > +unsigned long arch_scale_cpu_capacity(int cpu); > +#define arch_scale_cpu_capacity arch_scale_cpu_capacity > + > extern void arch_set_max_freq_ratio(bool turbo_disabled); > extern void freq_invariance_set_perf_ratio(u64 ratio, bool turbo_disabled); > #else > +static inline bool arch_enable_hybrid_capacity_scale(void) { return false; } > +static inline void arch_set_cpu_capacity(int cpu, unsigned long cap, > + unsigned long max_cap, > + unsigned long cap_freq, > + unsigned long base_freq) { } > + > static inline void arch_set_max_freq_ratio(bool turbo_disabled) { } > static inline void freq_invariance_set_perf_ratio(u64 ratio, bool turbo_disabled) { } > #endif > Index: linux-pm/arch/x86/kernel/cpu/aperfmperf.c > =================================================================== > --- linux-pm.orig/arch/x86/kernel/cpu/aperfmperf.c > +++ linux-pm/arch/x86/kernel/cpu/aperfmperf.c > @@ -349,9 +349,89 @@ static DECLARE_WORK(disable_freq_invaria > DEFINE_PER_CPU(unsigned long, arch_freq_scale) = SCHED_CAPACITY_SCALE; > EXPORT_PER_CPU_SYMBOL_GPL(arch_freq_scale); > > +static DEFINE_STATIC_KEY_FALSE(arch_hybrid_cap_scale_key); > + > +struct arch_hybrid_cpu_scale { > + unsigned long capacity; > + unsigned long freq_ratio; > +}; > + > +static struct arch_hybrid_cpu_scale __percpu *arch_cpu_scale; > + > +/** > + * arch_enable_hybrid_capacity_scale - Enable hybrid CPU capacity scaling > + * > + * Allocate memory for per-CPU data used by hybrid CPU capacity scaling, > + * initialize it and set the static key controlling its code paths. > + * > + * Must be called before arch_set_cpu_capacity(). > + */ > +bool arch_enable_hybrid_capacity_scale(void) > +{ > + int cpu; > + > + if (static_branch_unlikely(&arch_hybrid_cap_scale_key)) { > + WARN_ONCE(1, "Hybrid CPU capacity scaling already enabled"); > + return true; > + } > + > + arch_cpu_scale = alloc_percpu(struct arch_hybrid_cpu_scale); > + if (!arch_cpu_scale) > + return false; > + > + for_each_possible_cpu(cpu) { > + per_cpu_ptr(arch_cpu_scale, cpu)->capacity = SCHED_CAPACITY_SCALE; > + per_cpu_ptr(arch_cpu_scale, cpu)->freq_ratio = arch_max_freq_ratio; > + } > + > + static_branch_enable(&arch_hybrid_cap_scale_key); > + > + pr_info("Hybrid CPU capacity scaling enabled\n"); > + > + return true; > +} > + > +/** > + * arch_set_cpu_capacity - Set scale-invariance parameters for a CPU > + * @cpu: Target CPU. > + * @cap: Capacity of @cpu at its maximum frequency, relative to @max_cap. > + * @max_cap: System-wide maximum CPU capacity. > + * @cap_freq: Frequency of @cpu corresponding to @cap. > + * @base_freq: Frequency of @cpu at which MPERF counts. > + * > + * The units in which @cap and @max_cap are expressed do not matter, so long > + * as they are consistent, because the former is effectively divided by the > + * latter. Analogously for @cap_freq and @base_freq. > + * > + * After calling this function for all CPUs, call arch_rebuild_sched_domains() > + * to let the scheduler know that capacity-aware scheduling can be used going > + * forward. > + */ > +void arch_set_cpu_capacity(int cpu, unsigned long cap, unsigned long max_cap, > + unsigned long cap_freq, unsigned long base_freq) > +{ > + if (static_branch_likely(&arch_hybrid_cap_scale_key)) { > + WRITE_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->capacity, > + div_u64(cap << SCHED_CAPACITY_SHIFT, max_cap)); > + WRITE_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->freq_ratio, > + div_u64(cap_freq << SCHED_CAPACITY_SHIFT, base_freq)); > + } else { > + WARN_ONCE(1, "Hybrid CPU capacity scaling not enabled"); > + } > +} > + > +unsigned long arch_scale_cpu_capacity(int cpu) > +{ > + if (static_branch_unlikely(&arch_hybrid_cap_scale_key)) > + return READ_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->capacity); > + > + return SCHED_CAPACITY_SCALE; > +} > +EXPORT_SYMBOL_GPL(arch_scale_cpu_capacity); > + > static void scale_freq_tick(u64 acnt, u64 mcnt) > { > - u64 freq_scale; > + u64 freq_scale, freq_ratio; > > if (!arch_scale_freq_invariant()) > return; > @@ -359,7 +439,12 @@ static void scale_freq_tick(u64 acnt, u6 > if (check_shl_overflow(acnt, 2*SCHED_CAPACITY_SHIFT, &acnt)) > goto error; > > - if (check_mul_overflow(mcnt, arch_max_freq_ratio, &mcnt) || !mcnt) > + if (static_branch_unlikely(&arch_hybrid_cap_scale_key)) > + freq_ratio = READ_ONCE(this_cpu_ptr(arch_cpu_scale)->freq_ratio); > + else > + freq_ratio = arch_max_freq_ratio; > + > + if (check_mul_overflow(mcnt, freq_ratio, &mcnt) || !mcnt) > goto error; > > freq_scale = div64_u64(acnt, mcnt); > > >
On Wed, Aug 28, 2024 at 01:47:25PM +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > In order be able to compute the sizes of tasks consistently across all > CPUs in a hybrid system, it is necessary to provide CPU capacity scaling > information to the scheduler via arch_scale_cpu_capacity(). Moreover, > the value returned by arch_scale_freq_capacity() for the given CPU must > correspond to the arch_scale_cpu_capacity() return value for it, or > utilization computations will be inaccurate. > > Add support for it through per-CPU variables holding the capacity and > maximum-to-base frequency ratio (times SCHED_CAPACITY_SCALE) that will > be returned by arch_scale_cpu_capacity() and used by scale_freq_tick() > to compute arch_freq_scale for the current CPU, respectively. > > In order to avoid adding measurable overhead for non-hybrid x86 systems, > which are the vast majority in the field, whether or not the new hybrid > CPU capacity scaling will be in effect is controlled by a static key. > This static key is set by calling arch_enable_hybrid_capacity_scale() > which also allocates memory for the per-CPU data and initializes it. > Next, arch_set_cpu_capacity() is used to set the per-CPU variables > mentioned above for each CPU and arch_rebuild_sched_domains() needs > to be called for the scheduler to realize that capacity-aware > scheduling can be used going forward. > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > --- > > v2 -> v3: > * Rebase after dropping patch [1/3]. > * Rename arch_set_cpu_capacity() arguments. > * Add empty line to arch_enable_hybrid_capacity_scale(). > * Declare local variables in scale_freq_tick() on one line. > > v1 -> v2: > * Replaces WARN_ON_ONCE() with WARN_ONCE() (2 places) > * Fix arch_enable_hybrid_capacity_scale() return value when hybrid > capacity scaling is already enabled. > * Allow arch_enable_hybrid_capacity_scale() to succeed when > frequency-invariance is not enabled. > * Fix arch_set_cpu_capacity() kerneldoc comment > * Do not disable capacity scaling in disable_freq_invariance_workfn(). > * Relocate arch_hybrid_cap_scale_key definition. > > --- Only one minor comment below... FWIW: Reviewed-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> Tested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> # scale invariance [...] > + > +static struct arch_hybrid_cpu_scale __percpu *arch_cpu_scale; > + > +/** > + * arch_enable_hybrid_capacity_scale - Enable hybrid CPU capacity scaling This looks to me like a kernel-doc comment. The function name should have (). [...] > +/** > + * arch_set_cpu_capacity - Set scale-invariance parameters for a CPU Same here.
On Wed, Sep 4, 2024 at 8:17 AM Ricardo Neri <ricardo.neri-calderon@linux.intel.com> wrote: > > On Wed, Aug 28, 2024 at 01:47:25PM +0200, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > > > In order be able to compute the sizes of tasks consistently across all > > CPUs in a hybrid system, it is necessary to provide CPU capacity scaling > > information to the scheduler via arch_scale_cpu_capacity(). Moreover, > > the value returned by arch_scale_freq_capacity() for the given CPU must > > correspond to the arch_scale_cpu_capacity() return value for it, or > > utilization computations will be inaccurate. > > > > Add support for it through per-CPU variables holding the capacity and > > maximum-to-base frequency ratio (times SCHED_CAPACITY_SCALE) that will > > be returned by arch_scale_cpu_capacity() and used by scale_freq_tick() > > to compute arch_freq_scale for the current CPU, respectively. > > > > In order to avoid adding measurable overhead for non-hybrid x86 systems, > > which are the vast majority in the field, whether or not the new hybrid > > CPU capacity scaling will be in effect is controlled by a static key. > > This static key is set by calling arch_enable_hybrid_capacity_scale() > > which also allocates memory for the per-CPU data and initializes it. > > Next, arch_set_cpu_capacity() is used to set the per-CPU variables > > mentioned above for each CPU and arch_rebuild_sched_domains() needs > > to be called for the scheduler to realize that capacity-aware > > scheduling can be used going forward. > > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > --- > > > > v2 -> v3: > > * Rebase after dropping patch [1/3]. > > * Rename arch_set_cpu_capacity() arguments. > > * Add empty line to arch_enable_hybrid_capacity_scale(). > > * Declare local variables in scale_freq_tick() on one line. > > > > v1 -> v2: > > * Replaces WARN_ON_ONCE() with WARN_ONCE() (2 places) > > * Fix arch_enable_hybrid_capacity_scale() return value when hybrid > > capacity scaling is already enabled. > > * Allow arch_enable_hybrid_capacity_scale() to succeed when > > frequency-invariance is not enabled. > > * Fix arch_set_cpu_capacity() kerneldoc comment > > * Do not disable capacity scaling in disable_freq_invariance_workfn(). > > * Relocate arch_hybrid_cap_scale_key definition. > > > > --- > > Only one minor comment below... > > FWIW: > Reviewed-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> > Tested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> # scale invariance Thanks! > [...] > > > + > > +static struct arch_hybrid_cpu_scale __percpu *arch_cpu_scale; > > + > > +/** > > + * arch_enable_hybrid_capacity_scale - Enable hybrid CPU capacity scaling > > This looks to me like a kernel-doc comment. The function name should have (). Well, there are quite a few function kerneldoc comments without the parens at the end of the name, but sure. > [...] > > +/** > > + * arch_set_cpu_capacity - Set scale-invariance parameters for a CPU > > Same here.
Index: linux-pm/arch/x86/include/asm/topology.h =================================================================== --- linux-pm.orig/arch/x86/include/asm/topology.h +++ linux-pm/arch/x86/include/asm/topology.h @@ -282,9 +282,22 @@ static inline long arch_scale_freq_capac } #define arch_scale_freq_capacity arch_scale_freq_capacity +bool arch_enable_hybrid_capacity_scale(void); +void arch_set_cpu_capacity(int cpu, unsigned long cap, unsigned long max_cap, + unsigned long cap_freq, unsigned long base_freq); + +unsigned long arch_scale_cpu_capacity(int cpu); +#define arch_scale_cpu_capacity arch_scale_cpu_capacity + extern void arch_set_max_freq_ratio(bool turbo_disabled); extern void freq_invariance_set_perf_ratio(u64 ratio, bool turbo_disabled); #else +static inline bool arch_enable_hybrid_capacity_scale(void) { return false; } +static inline void arch_set_cpu_capacity(int cpu, unsigned long cap, + unsigned long max_cap, + unsigned long cap_freq, + unsigned long base_freq) { } + static inline void arch_set_max_freq_ratio(bool turbo_disabled) { } static inline void freq_invariance_set_perf_ratio(u64 ratio, bool turbo_disabled) { } #endif Index: linux-pm/arch/x86/kernel/cpu/aperfmperf.c =================================================================== --- linux-pm.orig/arch/x86/kernel/cpu/aperfmperf.c +++ linux-pm/arch/x86/kernel/cpu/aperfmperf.c @@ -349,9 +349,89 @@ static DECLARE_WORK(disable_freq_invaria DEFINE_PER_CPU(unsigned long, arch_freq_scale) = SCHED_CAPACITY_SCALE; EXPORT_PER_CPU_SYMBOL_GPL(arch_freq_scale); +static DEFINE_STATIC_KEY_FALSE(arch_hybrid_cap_scale_key); + +struct arch_hybrid_cpu_scale { + unsigned long capacity; + unsigned long freq_ratio; +}; + +static struct arch_hybrid_cpu_scale __percpu *arch_cpu_scale; + +/** + * arch_enable_hybrid_capacity_scale - Enable hybrid CPU capacity scaling + * + * Allocate memory for per-CPU data used by hybrid CPU capacity scaling, + * initialize it and set the static key controlling its code paths. + * + * Must be called before arch_set_cpu_capacity(). + */ +bool arch_enable_hybrid_capacity_scale(void) +{ + int cpu; + + if (static_branch_unlikely(&arch_hybrid_cap_scale_key)) { + WARN_ONCE(1, "Hybrid CPU capacity scaling already enabled"); + return true; + } + + arch_cpu_scale = alloc_percpu(struct arch_hybrid_cpu_scale); + if (!arch_cpu_scale) + return false; + + for_each_possible_cpu(cpu) { + per_cpu_ptr(arch_cpu_scale, cpu)->capacity = SCHED_CAPACITY_SCALE; + per_cpu_ptr(arch_cpu_scale, cpu)->freq_ratio = arch_max_freq_ratio; + } + + static_branch_enable(&arch_hybrid_cap_scale_key); + + pr_info("Hybrid CPU capacity scaling enabled\n"); + + return true; +} + +/** + * arch_set_cpu_capacity - Set scale-invariance parameters for a CPU + * @cpu: Target CPU. + * @cap: Capacity of @cpu at its maximum frequency, relative to @max_cap. + * @max_cap: System-wide maximum CPU capacity. + * @cap_freq: Frequency of @cpu corresponding to @cap. + * @base_freq: Frequency of @cpu at which MPERF counts. + * + * The units in which @cap and @max_cap are expressed do not matter, so long + * as they are consistent, because the former is effectively divided by the + * latter. Analogously for @cap_freq and @base_freq. + * + * After calling this function for all CPUs, call arch_rebuild_sched_domains() + * to let the scheduler know that capacity-aware scheduling can be used going + * forward. + */ +void arch_set_cpu_capacity(int cpu, unsigned long cap, unsigned long max_cap, + unsigned long cap_freq, unsigned long base_freq) +{ + if (static_branch_likely(&arch_hybrid_cap_scale_key)) { + WRITE_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->capacity, + div_u64(cap << SCHED_CAPACITY_SHIFT, max_cap)); + WRITE_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->freq_ratio, + div_u64(cap_freq << SCHED_CAPACITY_SHIFT, base_freq)); + } else { + WARN_ONCE(1, "Hybrid CPU capacity scaling not enabled"); + } +} + +unsigned long arch_scale_cpu_capacity(int cpu) +{ + if (static_branch_unlikely(&arch_hybrid_cap_scale_key)) + return READ_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->capacity); + + return SCHED_CAPACITY_SCALE; +} +EXPORT_SYMBOL_GPL(arch_scale_cpu_capacity); + static void scale_freq_tick(u64 acnt, u64 mcnt) { - u64 freq_scale; + u64 freq_scale, freq_ratio; if (!arch_scale_freq_invariant()) return; @@ -359,7 +439,12 @@ static void scale_freq_tick(u64 acnt, u6 if (check_shl_overflow(acnt, 2*SCHED_CAPACITY_SHIFT, &acnt)) goto error; - if (check_mul_overflow(mcnt, arch_max_freq_ratio, &mcnt) || !mcnt) + if (static_branch_unlikely(&arch_hybrid_cap_scale_key)) + freq_ratio = READ_ONCE(this_cpu_ptr(arch_cpu_scale)->freq_ratio); + else + freq_ratio = arch_max_freq_ratio; + + if (check_mul_overflow(mcnt, freq_ratio, &mcnt) || !mcnt) goto error; freq_scale = div64_u64(acnt, mcnt);