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Date: Thu, 10 Dec 2020 11:09:06 +0000 From: Ionela Voinescu <ionela.voinescu@....com> To: Viresh Kumar <viresh.kumar@...aro.org> Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Vincent Guittot <vincent.guittot@...aro.org>, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] arm64: topology: Avoid the static_branch_{enable|disable} dance On Thursday 10 Dec 2020 at 15:12:25 (+0530), Viresh Kumar wrote: > Avoid the static_branch_enable() and static_branch_disable() dance by > redoing the code in a different way. We will be fully invariant here > only if amu_fie_cpus is set with all present CPUs, use that instead of > yet another call to topology_scale_freq_invariant(). > > This also avoids running rest of the routine if we enabled the static > branch, followed by a disable. > > Also make the first call to topology_scale_freq_invariant() just when we > need it, instead of at the top of the routine. This makes it further > clear on why we need it, i.e. just around enabling AMUs use here. > > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org> > --- > arch/arm64/kernel/topology.c | 21 +++++++++------------ > 1 file changed, 9 insertions(+), 12 deletions(-) > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index 7f7d8de325b6..6dedc6ee91cf 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 invariance_status; > cpumask_var_t valid_cpus; > int ret = 0; > int cpu; > @@ -255,18 +255,15 @@ static int __init init_amu_fie(void) > 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); > - } This check verifies if there are *any* CPUs for which AMUs can be used for FIE (!empty mask) -> enable static key. > + /* Disallow partial use of counters for frequency invariance */ > + if (!cpumask_equal(amu_fie_cpus, cpu_present_mask)) > + goto free_valid_mask; > The replacement verifies if *all* present CPUs support AMUs for FIE and only then it enables the static key. Ionela. > - /* > - * If the system is not fully invariant after AMU init, disable > - * partial use of counters for frequency invariance. > - */ > - if (!topology_scale_freq_invariant()) > - static_branch_disable(&amu_fie_key); > + pr_info("CPUs[%*pbl]: counters will be used for FIE.", > + cpumask_pr_args(amu_fie_cpus)); > + > + invariance_status = topology_scale_freq_invariant(); > + static_branch_enable(&amu_fie_key); > > /* > * Task scheduler behavior depends on frequency invariance support, > -- > 2.25.0.rc1.19.g042ed3e048af >
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