Messages in this thread Patch in this message | | | From | Srikar Dronamraju <> | Subject | [PATCH v4 1/5] powerpc/smp: Enable Asym packing for cores on shared processor | Date | Thu, 9 Nov 2023 11:19:29 +0530 |
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If there are shared processor LPARs, underlying Hypervisor can have more virtual cores to handle than actual physical cores.
Starting with Power 9, a big core (aka SMT8 core) has 2 nearly independent thread groups. On a shared processors LPARs, it helps to pack threads to lesser number of cores so that the overall system performance and utilization improves. PowerVM schedules at a big core level. Hence packing to fewer cores helps.
For example: Lets says there are two 8-core Shared LPARs that are actually sharing a 8 Core shared physical pool, each running 8 threads each. Then Consolidating 8 threads to 4 cores on each LPAR would help them to perform better. This is because each of the LPAR will get 100% time to run applications and there will no switching required by the Hypervisor.
To achieve this, enable SD_ASYM_PACKING flag at CACHE, MC and DIE level when the system is running in shared processor mode and has big cores.
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> --- Changelog: v3 -> v4: - Dont use splpar_asym_pack with SMT - Conflict resolution due to rebase (DIE changed to PKG) v2 -> v3: - Handle comments from Michael Ellerman. - Rework using existing cpu_has_features static key v1->v2: Using Jump label instead of a variable.
arch/powerpc/kernel/smp.c | 37 +++++++++++++++++++++++++++++-------- 1 file changed, 29 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c index ab691c89d787..69a3262024f1 100644 --- a/arch/powerpc/kernel/smp.c +++ b/arch/powerpc/kernel/smp.c @@ -993,16 +993,20 @@ static bool shared_caches; /* cpumask of CPUs with asymmetric SMT dependency */ static int powerpc_smt_flags(void) { - int flags = SD_SHARE_CPUCAPACITY | SD_SHARE_PKG_RESOURCES; + if (!cpu_has_feature(CPU_FTR_ASYM_SMT)) + return SD_SHARE_CPUCAPACITY | SD_SHARE_PKG_RESOURCES; - if (cpu_has_feature(CPU_FTR_ASYM_SMT)) { - printk_once(KERN_INFO "Enabling Asymmetric SMT scheduling\n"); - flags |= SD_ASYM_PACKING; - } - return flags; + return SD_SHARE_CPUCAPACITY | SD_SHARE_PKG_RESOURCES | SD_ASYM_PACKING; } #endif +/* + * On shared processor LPARs scheduled on a big core (which has two or more + * independent thread groups per core), prefer lower numbered CPUs, so + * that workload consolidates to lesser number of cores. + */ +static __ro_after_init DEFINE_STATIC_KEY_FALSE(splpar_asym_pack); + /* * P9 has a slightly odd architecture where pairs of cores share an L2 cache. * This topology makes it *much* cheaper to migrate tasks between adjacent cores @@ -1011,9 +1015,20 @@ static int powerpc_smt_flags(void) */ static int powerpc_shared_cache_flags(void) { + if (static_branch_unlikely(&splpar_asym_pack)) + return SD_SHARE_PKG_RESOURCES | SD_ASYM_PACKING; + return SD_SHARE_PKG_RESOURCES; } +static int powerpc_shared_proc_flags(void) +{ + if (static_branch_unlikely(&splpar_asym_pack)) + return SD_ASYM_PACKING; + + return 0; +} + /* * We can't just pass cpu_l2_cache_mask() directly because * returns a non-const pointer and the compiler barfs on that. @@ -1050,8 +1065,8 @@ static struct sched_domain_topology_level powerpc_topology[] = { { cpu_smt_mask, powerpc_smt_flags, SD_INIT_NAME(SMT) }, #endif { shared_cache_mask, powerpc_shared_cache_flags, SD_INIT_NAME(CACHE) }, - { cpu_mc_mask, SD_INIT_NAME(MC) }, - { cpu_cpu_mask, SD_INIT_NAME(PKG) }, + { cpu_mc_mask, powerpc_shared_proc_flags, SD_INIT_NAME(MC) }, + { cpu_cpu_mask, powerpc_shared_proc_flags, SD_INIT_NAME(PKG) }, { NULL, }, }; @@ -1686,7 +1701,13 @@ static void __init fixup_topology(void) { int i; + if (is_shared_processor() && has_big_cores) + static_branch_enable(&splpar_asym_pack); + #ifdef CONFIG_SCHED_SMT + if (cpu_has_feature(CPU_FTR_ASYM_SMT)) + pr_info_once("Enabling Asymmetric SMT scheduling\n"); + if (has_big_cores) { pr_info("Big cores detected but using small core scheduling\n"); powerpc_topology[smt_idx].mask = smallcore_smt_mask; -- 2.31.1
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