[PATCH 13/17] powerpc: enable/disable paravirt CPUs based on steal time
From: Shrikanth Hegde <hidden>
Date: 2025-11-19 12:46:25
Also in:
lkml
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Michael Ellerman, Linus Torvalds
available_cores - Number of cores LPAR(VM) can use at this moment. remaining cores will have CPUs marked as paravirt. This follow stepwise approach for reducing/increasing the number of available_cores. Very simple Logic. if (steal_time > high_threshold) available_cores-- if (steal_time < low_threshould) available_cores++ It also check previous direction taken to avoid un-necessary ping-pongs. Note: It works well only when CPUs are spread out equal numbered across NUMA nodes. Originally-by: Srikar Dronamraju [off-list ref] Signed-off-by: Shrikanth Hegde <redacted> --- arch/powerpc/platforms/pseries/lpar.c | 53 ++++++++++++++++++++++++ arch/powerpc/platforms/pseries/pseries.h | 1 + 2 files changed, 54 insertions(+)
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 935fced6e127..825b5b4e2b43 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c@@ -43,6 +43,7 @@ #include <asm/fadump.h> #include <asm/dtl.h> #include <asm/vphn.h> +#include <linux/sched/isolation.h> #include "pseries.h"
@@ -2056,6 +2057,58 @@ void pseries_init_ec_vp_cores(void) /* Initialize the available cores to all VP initially */ available_cores = max(entitled_cores, virtual_procs); } + +#define STEAL_RATIO_HIGH 400 +#define STEAL_RATIO_LOW 150 + +void update_soft_entitlement(unsigned long steal_ratio) +{ + static int prev_direction; + int cpu; + + if (!entitled_cores) + return; + + if (steal_ratio >= STEAL_RATIO_HIGH && prev_direction > 0) { + /* + * System entitlement was reduced earlier but we continue to + * see steal time. Reduce entitlement further. + */ + if (available_cores == entitled_cores) + return; + + /* Mark them paravirt, enable tick if it is nohz_full */ + for (cpu = (available_cores - 1) * threads_per_core; + cpu < available_cores * threads_per_core; cpu++) { + set_cpu_paravirt(cpu, true); + if (tick_nohz_full_cpu(cpu)) + tick_nohz_dep_set_cpu(cpu, TICK_DEP_BIT_SCHED); + } + available_cores--; + + } else if (steal_ratio <= STEAL_RATIO_LOW && prev_direction < 0) { + /* + * System entitlement was increased but we continue to see + * less steal time. Increase entitlement further. + */ + if (available_cores == virtual_procs) + return; + + /* mark them avaialble */ + for (cpu = available_cores * threads_per_core; + cpu < (available_cores + 1) * threads_per_core; cpu++) + set_cpu_paravirt(cpu, false); + + available_cores++; + } + if (steal_ratio >= STEAL_RATIO_HIGH) + prev_direction = 1; + else if (steal_ratio <= STEAL_RATIO_LOW) + prev_direction = -1; + else + prev_direction = 0; +} #else void pseries_init_ec_vp_cores(void) { return; } +void update_soft_entitlement(unsigned long steal_ratio) { return; } #endif
diff --git a/arch/powerpc/platforms/pseries/pseries.h b/arch/powerpc/platforms/pseries/pseries.h
index 3968a6970fa8..d1f9ec77ff57 100644
--- a/arch/powerpc/platforms/pseries/pseries.h
+++ b/arch/powerpc/platforms/pseries/pseries.h@@ -115,6 +115,7 @@ int dlpar_workqueue_init(void); extern u32 pseries_security_flavor; void pseries_setup_security_mitigations(void); +void update_soft_entitlement(unsigned long steal_ratio); #ifdef CONFIG_PPC_64S_HASH_MMU void pseries_lpar_read_hblkrm_characteristics(void);
--
2.47.3