On Tue, Jul 14, 2020 at 10:06:19AM +0530, Srikar Dronamraju wrote:
> Currently "CACHE" domain happens to be the 2nd sched domain as per
> powerpc_topology. This domain will collapse if cpumask of l2-cache is
> same as SMT domain. However we could generalize this domain such that it
> could mean either be a "CACHE" domain or a "BIGCORE" domain.
>
> While setting up the "CACHE" domain, check if shared_cache is already
> set.
>
> Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
> Cc: Michael Ellerman <micha...@au1.ibm.com>
> Cc: Nick Piggin <npig...@au1.ibm.com>
> Cc: Oliver OHalloran <olive...@au1.ibm.com>
> Cc: Nathan Lynch <nath...@linux.ibm.com>
> Cc: Michael Neuling <mi...@linux.ibm.com>
> Cc: Anton Blanchard <an...@au1.ibm.com>
> Cc: Gautham R Shenoy <e...@linux.vnet.ibm.com>
> Cc: Vaidyanathan Srinivasan <sva...@linux.ibm.com>
> Signed-off-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/smp.c | 48 +++++++++++++++++++++++++++------------
> 1 file changed, 34 insertions(+), 14 deletions(-)
>
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index 875f57e41355..f8faf75135af 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -85,6 +85,14 @@ EXPORT_PER_CPU_SYMBOL(cpu_l2_cache_map);
> EXPORT_PER_CPU_SYMBOL(cpu_core_map);
> EXPORT_SYMBOL_GPL(has_big_cores);
>
> +enum {
> +#ifdef CONFIG_SCHED_SMT
> + smt_idx,
> +#endif
> + bigcore_idx,
> + die_idx,
> +};
> +
> #define MAX_THREAD_LIST_SIZE 8
> #define THREAD_GROUP_SHARE_L1 1
> struct thread_groups {
> @@ -851,13 +859,7 @@ static int powerpc_shared_cache_flags(void)
> */
> static const struct cpumask *shared_cache_mask(int cpu)
> {
> - if (shared_caches)
> - return cpu_l2_cache_mask(cpu);
> -
> - if (has_big_cores)
> - return cpu_smallcore_mask(cpu);
> -
> - return cpu_smt_mask(cpu);
> + return per_cpu(cpu_l2_cache_map, cpu);
> }
>
> #ifdef CONFIG_SCHED_SMT
> @@ -867,11 +869,16 @@ static const struct cpumask *smallcore_smt_mask(int cpu)
> }
> #endif
>
> +static const struct cpumask *cpu_bigcore_mask(int cpu)
> +{
> + return cpu_core_mask(cpu);
It should be cpu_smt_mask() if we want the redundant big-core to be
degenerated in favour of the SMT level on P8, no? Because
cpu_core_mask refers to all the CPUs that are in the same chip.
> +}
> +
> static struct sched_domain_topology_level powerpc_topology[] = {
> #ifdef CONFIG_SCHED_SMT
> { cpu_smt_mask, powerpc_smt_flags, SD_INIT_NAME(SMT) },
> #endif
> - { shared_cache_mask, powerpc_shared_cache_flags, SD_INIT_NAME(CACHE) },
> + { cpu_bigcore_mask, SD_INIT_NAME(BIGCORE) },
> { cpu_cpu_mask, SD_INIT_NAME(DIE) },
> { NULL, },
> };
> @@ -895,7 +902,7 @@ static int init_big_cores(void)
>
> #ifdef CONFIG_SCHED_SMT
> pr_info("Big cores detected. Using small core scheduling\n");
> - powerpc_topology[0].mask = smallcore_smt_mask;
> + powerpc_topology[smt_idx].mask = smallcore_smt_mask;
> #endif
>
> return 0;
> @@ -1319,7 +1326,6 @@ 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;
> @@ -1345,14 +1351,20 @@ 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;
Shouldn't we use cpumask_subset() here ?
> + }
>
> set_numa_node(numa_cpu_lookup_table[cpu]);
> set_numa_mem(local_memory_node(numa_cpu_lookup_table[cpu]));
> @@ -1390,6 +1402,14 @@ void __init smp_cpus_done(unsigned int max_cpus)
> smp_ops->bringup_done();
>
> dump_numa_cpu_topology();
> + if (shared_caches) {
> + pr_info("Using shared cache scheduler topology\n");
> + powerpc_topology[bigcore_idx].mask = shared_cache_mask;
> +#ifdef CONFIG_SCHED_DEBUG
> + powerpc_topology[bigcore_idx].name = "CACHE";
> +#endif
> + powerpc_topology[bigcore_idx].sd_flags =
> powerpc_shared_cache_flags;
> + }
I would much rather that we have all the topology-fixups done in one
function.
fixup_topology(void) {
if (has_big_core)
powerpc_topology[smt_idx].mask = smallcore_smt_mask;
if (shared_caches) {
const char *name = "CACHE";
powerpc_topology[bigcore_idx].mask = shared_cache_mask;
strlcpy(powerpc_topology[bigcore_idx].name, name,
strlen(name));
powerpc_topology[bigcore_idx].sd_flags = powerpc_shared_cache_flags;
}
/* Any other changes to the topology structure here */
And also as an optimization, get rid of degenerate structures here
itself so that we don't pay additional penalty while building the
sched-domains each time.
}
>
> set_sched_topology(powerpc_topology);
> }
> --
> 2.17.1
>
