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| author | Paul Mackerras <paulus@ozlabs.org> | 2017-02-06 13:24:41 +1100 |
|---|---|---|
| committer | Paul Mackerras <paulus@ozlabs.org> | 2017-06-19 14:34:20 +1000 |
| commit | 3c313524605a6afd8207448a8e9967f5e8cba734 (patch) | |
| tree | 618ce202f550dccba853ec66b75c973a976cf833 /Documentation | |
| parent | 769377f77ca2087baeaf97ce0b7026abeba3b581 (diff) | |
| download | linux-3c313524605a6afd8207448a8e9967f5e8cba734.tar.gz | |
KVM: PPC: Book3S HV: Allow userspace to set the desired SMT mode
This allows userspace to set the desired virtual SMT (simultaneous multithreading) mode for a VM, that is, the number of VCPUs that get assigned to each virtual core. Previously, the virtual SMT mode was fixed to the number of threads per subcore, and if userspace wanted to have fewer vcpus per vcore, then it would achieve that by using a sparse CPU numbering. This had the disadvantage that the vcpu numbers can get quite large, particularly for SMT1 guests on a POWER8 with 8 threads per core. With this patch, userspace can set its desired virtual SMT mode and then use contiguous vcpu numbering. On POWER8, where the threading mode is "strict", the virtual SMT mode must be less than or equal to the number of threads per subcore. On POWER9, which implements a "loose" threading mode, the virtual SMT mode can be any power of 2 between 1 and 8, even though there is effectively one thread per subcore, since the threads are independent and can all be in different partitions. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/virtual/kvm/api.txt | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index 4029943887a3..68b66b538d2d 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -3996,6 +3996,21 @@ Parameters: none Allow use of adapter-interruption suppression. Returns: 0 on success; -EBUSY if a VCPU has already been created. +7.11 KVM_CAP_PPC_SMT + +Architectures: ppc +Parameters: vsmt_mode, flags + +Enabling this capability on a VM provides userspace with a way to set +the desired virtual SMT mode (i.e. the number of virtual CPUs per +virtual core). The virtual SMT mode, vsmt_mode, must be a power of 2 +between 1 and 8. On POWER8, vsmt_mode must also be no greater than +the number of threads per subcore for the host. Currently flags must +be 0. A successful call to enable this capability will result in +vsmt_mode being returned when the KVM_CAP_PPC_SMT capability is +subsequently queried for the VM. This capability is only supported by +HV KVM, and can only be set before any VCPUs have been created. + 8. Other capabilities. ---------------------- |