| Message ID | 202f775d57bd143602f9100ba3d9619d15d43409.1607617625.git.viresh.kumar@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V2,1/2] arm64: topology: Avoid the have_policy check | expand |
Hey, On Thursday 10 Dec 2020 at 21:59:23 (+0530), Viresh Kumar wrote: > This patch does a couple of optimizations in init_amu_fie(), like early > exits from paths where we don't need to continue any further, moving the > calls to topology_scale_freq_invariant() just when we need > them, instead of at the top of the routine, and avoiding calling it for > the third time. > > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> > --- > V2: > - The enable/disable dance is actually required, just made a bunch of > other optimizations to make it look better. > > arch/arm64/kernel/topology.c | 22 ++++++++++++++-------- > 1 file changed, 14 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index ebadc73449f9..1ebdb667f0d1 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -221,7 +221,7 @@ static DEFINE_STATIC_KEY_FALSE(amu_fie_key); > > static int __init init_amu_fie(void) > { > - bool invariance_status = topology_scale_freq_invariant(); > + bool prev, now; Nit: can you move this below valid_cpus? It makes the section nicer if they are in decreasing order of line length. > cpumask_var_t valid_cpus; > int ret = 0; > int cpu; > @@ -249,18 +249,24 @@ static int __init init_amu_fie(void) > if (cpumask_equal(valid_cpus, cpu_present_mask)) > cpumask_copy(amu_fie_cpus, cpu_present_mask); > > - if (!cpumask_empty(amu_fie_cpus)) { > - pr_info("CPUs[%*pbl]: counters will be used for FIE.", > - cpumask_pr_args(amu_fie_cpus)); > - static_branch_enable(&amu_fie_key); > - } > + if (cpumask_empty(amu_fie_cpus)) > + goto free_valid_mask; > + > + prev = topology_scale_freq_invariant(); > + static_branch_enable(&amu_fie_key); I think there could be a potential problem here (it would be unlikely but why not fix it :) ). It was in the code before your changes. When we enable amu_fie_key here, topology_scale_freq_tick() could be called for AMU CPUs, which will compute and set a scale factor. Later on, if we happen to find the system not invariant, we disable counter based invariance, but a scale factor might have been set already for a CPU, which would and should have returned 1024 otherwise (the initialisation value of freq_scale). Therefore, while here, you could instead do the following: cpufreq_inv = cpufreq_supports_freq_invariance(); if (!cpufreq_inv && !cpumask_subset(cpu_online_mask, amu_fie_cpus)) goto free_valid_mask; static_branch_enable(&amu_fie_key); pr_info(..); if (!cpufreq_inv) rebuild_sched_domains_energy(); What do you think? I can submit this separately, if you don't want the hassle. Thanks, Ionela. > + now = topology_scale_freq_invariant(); > > /* > * If the system is not fully invariant after AMU init, disable > * partial use of counters for frequency invariance. > */ > - if (!topology_scale_freq_invariant()) > + if (!now) { > static_branch_disable(&amu_fie_key); > + goto free_valid_mask; > + } > + > + pr_info("CPUs[%*pbl]: counters will be used for FIE.", > + cpumask_pr_args(amu_fie_cpus)); > > /* > * Task scheduler behavior depends on frequency invariance support, > @@ -268,7 +274,7 @@ static int __init init_amu_fie(void) > * a result of counter initialisation and use, retrigger the build of > * scheduling domains to ensure the information is propagated properly. > */ > - if (invariance_status != topology_scale_freq_invariant()) > + if (prev != now) > rebuild_sched_domains_energy(); > > free_valid_mask: > -- > 2.25.0.rc1.19.g042ed3e048af >
On 14-12-20, 14:00, Ionela Voinescu wrote: > I think there could be a potential problem here (it would be unlikely > but why not fix it :) ). It was in the code before your changes. > > When we enable amu_fie_key here, topology_scale_freq_tick() could be > called for AMU CPUs, which will compute and set a scale factor. Later > on, if we happen to find the system not invariant, we disable counter > based invariance, but a scale factor might have been set already for a > CPU, which would and should have returned 1024 otherwise (the > initialisation value of freq_scale). > > > Therefore, while here, you could instead do the following: > > cpufreq_inv = cpufreq_supports_freq_invariance(); > > if (!cpufreq_inv && > !cpumask_subset(cpu_online_mask, amu_fie_cpus)) > goto free_valid_mask; > > static_branch_enable(&amu_fie_key); > > pr_info(..); > > if (!cpufreq_inv) > rebuild_sched_domains_energy(); > > What do you think? I already had a patch for this, but for a different reason, i.e. to avoid the enable/disable dance. /* We aren't fully invariant yet */ if (!prev && !cpumask_equal(amu_fie_cpus, cpu_present_mask)) return; And this is quite similar to what you have here.
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c index ebadc73449f9..1ebdb667f0d1 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -221,7 +221,7 @@ static DEFINE_STATIC_KEY_FALSE(amu_fie_key); static int __init init_amu_fie(void) { - bool invariance_status = topology_scale_freq_invariant(); + bool prev, now; cpumask_var_t valid_cpus; int ret = 0; int cpu; @@ -249,18 +249,24 @@ static int __init init_amu_fie(void) if (cpumask_equal(valid_cpus, cpu_present_mask)) cpumask_copy(amu_fie_cpus, cpu_present_mask); - if (!cpumask_empty(amu_fie_cpus)) { - pr_info("CPUs[%*pbl]: counters will be used for FIE.", - cpumask_pr_args(amu_fie_cpus)); - static_branch_enable(&amu_fie_key); - } + if (cpumask_empty(amu_fie_cpus)) + goto free_valid_mask; + + prev = topology_scale_freq_invariant(); + static_branch_enable(&amu_fie_key); + now = topology_scale_freq_invariant(); /* * If the system is not fully invariant after AMU init, disable * partial use of counters for frequency invariance. */ - if (!topology_scale_freq_invariant()) + if (!now) { static_branch_disable(&amu_fie_key); + goto free_valid_mask; + } + + pr_info("CPUs[%*pbl]: counters will be used for FIE.", + cpumask_pr_args(amu_fie_cpus)); /* * Task scheduler behavior depends on frequency invariance support, @@ -268,7 +274,7 @@ static int __init init_amu_fie(void) * a result of counter initialisation and use, retrigger the build of * scheduling domains to ensure the information is propagated properly. */ - if (invariance_status != topology_scale_freq_invariant()) + if (prev != now) rebuild_sched_domains_energy(); free_valid_mask:
This patch does a couple of optimizations in init_amu_fie(), like early exits from paths where we don't need to continue any further, moving the calls to topology_scale_freq_invariant() just when we need them, instead of at the top of the routine, and avoiding calling it for the third time. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> --- V2: - The enable/disable dance is actually required, just made a bunch of other optimizations to make it look better. arch/arm64/kernel/topology.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-)