linux-kernel - [PATCH v2 0/3] KVM: s390: Couple of small cmpxchg() optimizations

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Message-ID: <20241126102515.3178914-1-hca@linux.ibm.com>
Date: Tue, 26 Nov 2024 11:25:12 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>
Cc: kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/3] KVM: s390: Couple of small cmpxchg() optimizations

v2:
- Replace broken WRITE_ONCE(..., 9) with intended WRITE_ONCE(..., 0).

v1:
Use try_cmpxchg() instead of cmpxchg() so compilers with flag output
operand support (gcc 14 and newer) can generate slightly better code.

Also get rid of two cmpxchg() usages on one/two byte memory areas
which generates inefficient code.

bloat-o-meter statistics of the kvm module:

add/remove: 0/0 grow/shrink: 0/11 up/down: 0/-318 (-318)
Function                                     old     new   delta
kvm_s390_handle_wait                         886     880      -6
kvm_s390_gisa_destroy                        226     220      -6
kvm_s390_gisa_clear                           96      90      -6
ipte_unlock                                  380     372      -8
kvm_s390_gisc_unregister                     270     260     -10
kvm_s390_gisc_register                       290     280     -10
gisa_vcpu_kicker                             200     190     -10
account_mem                                  250     232     -18
ipte_lock                                    416     368     -48
kvm_s390_update_topology_change_report       174     122     -52
kvm_s390_clear_local_irqs                    420     276    -144
Total: Before=316521, After=316203, chg -0.10%

Heiko Carstens (3):
  KVM: s390: Use try_cmpxchg() instead of cmpxchg() loops
  KVM: s390: Remove one byte cmpxchg() usage
  KVM: s390: Increase size of union sca_utility to four bytes

 arch/s390/include/asm/kvm_host.h | 10 +++++-----
 arch/s390/kvm/gaccess.c          | 16 ++++++++--------
 arch/s390/kvm/interrupt.c        | 25 ++++++++-----------------
 arch/s390/kvm/kvm-s390.c         |  4 ++--
 arch/s390/kvm/pci.c              |  5 ++---
 5 files changed, 25 insertions(+), 35 deletions(-)

-- 
2.45.2