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SubjectRe: [PATCH v5 06/10] powerpc/smp: Optimize start_secondary
Hi Srikar,

On Mon, Aug 10, 2020 at 12:48:30PM +0530, Srikar Dronamraju wrote:
> In start_secondary, even if shared_cache was already set, system does a
> redundant match for cpumask. This redundant check can be removed by
> checking if shared_cache is already set.
>
> While here, localize the sibling_mask variable to within the if
> condition.
>
> Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
> Cc: LKML <linux-kernel@vger.kernel.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Anton Blanchard <anton@ozlabs.org>
> Cc: Oliver O'Halloran <oohall@gmail.com>
> Cc: Nathan Lynch <nathanl@linux.ibm.com>
> Cc: Michael Neuling <mikey@neuling.org>
> Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Valentin Schneider <valentin.schneider@arm.com>
> Cc: Jordan Niethe <jniethe5@gmail.com>
> Cc: Vaidyanathan Srinivasan <svaidy@linux.ibm.com>
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

The change looks good to me.

Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>

> ---
> Changelog v4 ->v5:
> Retain cache domain, no need for generalization
> (Michael Ellerman, Peter Zijlstra,
> Valentin Schneider, Gautham R. Shenoy)
>
> Changelog v1 -> v2:
> Moved shared_cache topology fixup to fixup_topology (Gautham)
>
> arch/powerpc/kernel/smp.c | 17 +++++++++++------
> 1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index 0c960ce3be42..91cf5d05e7ec 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -851,7 +851,7 @@ static int powerpc_shared_cache_flags(void)
> */
> static const struct cpumask *shared_cache_mask(int cpu)
> {
> - return cpu_l2_cache_mask(cpu);
> + return per_cpu(cpu_l2_cache_map, cpu);
> }
>
> #ifdef CONFIG_SCHED_SMT
> @@ -1305,7 +1305,6 @@ static void add_cpu_to_masks(int cpu)
> void start_secondary(void *unused)
> {
> unsigned int cpu = smp_processor_id();
> - struct cpumask *(*sibling_mask)(int) = cpu_sibling_mask;
>
> mmgrab(&init_mm);
> current->active_mm = &init_mm;
> @@ -1331,14 +1330,20 @@ void start_secondary(void *unused)
> /* Update topology CPU masks */
> add_cpu_to_masks(cpu);
>
> - if (has_big_cores)
> - sibling_mask = cpu_smallcore_mask;
> /*
> * Check for any shared caches. Note that this must be done on a
> * per-core basis because one core in the pair might be disabled.
> */
> - if (!cpumask_equal(cpu_l2_cache_mask(cpu), sibling_mask(cpu)))
> - shared_caches = true;
> + if (!shared_caches) {
> + struct cpumask *(*sibling_mask)(int) = cpu_sibling_mask;
> + struct cpumask *mask = cpu_l2_cache_mask(cpu);
> +
> + if (has_big_cores)
> + sibling_mask = cpu_smallcore_mask;
> +
> + if (cpumask_weight(mask) > cpumask_weight(sibling_mask(cpu)))
> + shared_caches = true;
> + }
>
> set_numa_node(numa_cpu_lookup_table[cpu]);
> set_numa_mem(local_memory_node(numa_cpu_lookup_table[cpu]));
> --
> 2.18.2
>

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