diff options
| author | Andrea Righi <arighi@nvidia.com> | 2026-09-29 18:54:41 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-10-01 14:00:35 +0200 |
| commit | 648d44bda7314ffb5805f2bea8910b4cdccaecd0 (patch) | |
| tree | 934947f176154eee6be90577b008adea32951120 /kernel | |
| parent | c8fc4136fd3c58458592b77168f0916d08dbea5a (diff) | |
| download | linux-next-648d44bda7314ffb5805f2bea8910b4cdccaecd0.tar.gz linux-next-648d44bda7314ffb5805f2bea8910b4cdccaecd0.zip | |
sched/topology: Add asymmetric SMT packing override
Architectures can use SD_ASYM_PACKING to describe preferred CPU ordering
at the SMT scheduling domain. Some systems benefit from this policy, but
their firmware cannot describe the preference and inferring it from the
CPU model would embed a platform-specific policy in the kernel.
Add sched_smt_asym_packing=on boot option to force SD_ASYM_PACKING at
the SMT level. Omitting the option preserves the topology provided by
the architecture or firmware.
Apply the override centrally to domains with SD_SHARE_CPUCAPACITY so it
also covers architectures with custom SMT topology callbacks, including
powerpc.
When enabled, priority remains defined by arch_asym_cpu_priority(). The
weak default prefers lower-numbered logical CPUs, while architecture
overrides remain authoritative. Siblings with equal priorities remain
unordered. In particular, x86 with CONFIG_SCHED_MC_PRIO normally gives
both SMT siblings the same core priority, so enabling the option there
does not prioritize a sibling.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260929165538.726616-3-arighi@nvidia.com
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/topology.c | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 0248227d983a..dd2b1d70ec9d 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -32,6 +32,20 @@ static int __init sched_debug_setup(char *str) } early_param("sched_verbose", sched_debug_setup); +#ifdef CONFIG_SCHED_SMT +static bool sched_smt_asym_packing __read_mostly; + +static int __init setup_sched_smt_asym_packing(char *str) +{ + if (strcmp(str, "on")) + return 0; + + sched_smt_asym_packing = true; + return 1; +} +__setup("sched_smt_asym_packing=", setup_sched_smt_asym_packing); +#endif + static inline bool sched_debug(void) { return sched_debug_verbose; @@ -1950,6 +1964,10 @@ sd_init(struct sched_domain_topology_level *tl, if (WARN_ONCE(sd_flags & ~TOPOLOGY_SD_FLAGS, "wrong sd_flags in topology description\n")) sd_flags &= TOPOLOGY_SD_FLAGS; +#ifdef CONFIG_SCHED_SMT + if (sched_smt_asym_packing && (sd_flags & SD_SHARE_CPUCAPACITY)) + sd_flags |= SD_ASYM_PACKING; +#endif sd_flags |= asym_cpu_capacity_classify(sd_span, cpu_map); *sd = (struct sched_domain){ |