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 <[email protected]>
> ---
> 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
>
