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| author | Heiko Carstens <hca@linux.ibm.com> | 2024-11-26 11:25:15 +0100 |
|---|---|---|
| committer | Heiko Carstens <hca@linux.ibm.com> | 2024-11-27 12:55:15 +0100 |
| commit | f93d6d62e4697b0df1474f0b1314c3c158335f0a (patch) | |
| tree | 204e0771addf59df2ca7f9b2cfcb94ebbd814ea3 /arch | |
| parent | 7061c63919bde3bb0daa63e700a117ab1f2c97b1 (diff) | |
| download | lwn-f93d6d62e4697b0df1474f0b1314c3c158335f0a.tar.gz lwn-f93d6d62e4697b0df1474f0b1314c3c158335f0a.zip | |
KVM: s390: Increase size of union sca_utility to four bytes
kvm_s390_update_topology_change_report() modifies a single bit within
sca_utility using cmpxchg(). Given that the size of the sca_utility union
is two bytes this generates very inefficient code. Change the size to four
bytes, so better code can be generated.
Even though the size of sca_utility doesn't reflect architecture anymore
this seems to be the easiest and most pragmatic approach to avoid
inefficient code.
Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20241126102515.3178914-4-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/s390/include/asm/kvm_host.h | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h index 51201b4ac93a..7ef37f746d47 100644 --- a/arch/s390/include/asm/kvm_host.h +++ b/arch/s390/include/asm/kvm_host.h @@ -94,11 +94,16 @@ union ipte_control { }; }; +/* + * Utility is defined as two bytes but having it four bytes wide + * generates more efficient code. Since the following bytes are + * reserved this makes no functional difference. + */ union sca_utility { - __u16 val; + __u32 val; struct { - __u16 mtcr : 1; - __u16 reserved : 15; + __u32 mtcr : 1; + __u32 : 31; }; }; @@ -107,7 +112,7 @@ struct bsca_block { __u64 reserved[5]; __u64 mcn; union sca_utility utility; - __u8 reserved2[6]; + __u8 reserved2[4]; struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS]; }; @@ -115,7 +120,7 @@ struct esca_block { union ipte_control ipte_control; __u64 reserved1[6]; union sca_utility utility; - __u8 reserved2[6]; + __u8 reserved2[4]; __u64 mcn[4]; __u64 reserved3[20]; struct esca_entry cpu[KVM_S390_ESCA_CPU_SLOTS]; |