diff options
| author | Heiko Carstens | 2019-11-29 12:59:59 +0100 |
|---|---|---|
| committer | Vasily Gorbik | 2019-12-11 19:53:24 +0100 |
| commit | 1b68ac8678a8e9993deebd55014cbe803e78ca02 (patch) | |
| tree | 238e1b770590a25cc218e4437ea574278e4db246 /arch/s390/kernel | |
| parent | 157309a97015d8b32d65847d8a6d493d1a958e93 (diff) | |
s390: remove last diag 0x44 caller
diag 0x44 is a voluntary undirected yield of a virtual CPU. This has
caused a lot of performance issues in the past.
There is only one caller left, and that one is only executed if diag
0x9c (directed yield) is not present. Given that all hypervisors
implement diag 0x9c anyway, remove the last diag 0x44 to avoid that
more callers will be added.
Worst case that could happen now, if diag 0x9c is not present, is that
a virtual CPU would loop a bit instead of giving its time slice up.
diag 0x44 statistics in debugfs are kept and will always be zero, so
that user space can tell that there are no calls.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'arch/s390/kernel')
| -rw-r--r-- | arch/s390/kernel/early.c | 16 | ||||
| -rw-r--r-- | arch/s390/kernel/smp.c | 13 |
2 files changed, 5 insertions, 24 deletions
diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c index db32a55daaec..cd241ee66eff 100644 --- a/arch/s390/kernel/early.c +++ b/arch/s390/kernel/early.c @@ -204,21 +204,6 @@ static __init void detect_diag9c(void) S390_lowcore.machine_flags |= MACHINE_FLAG_DIAG9C; } -static __init void detect_diag44(void) -{ - int rc; - - diag_stat_inc(DIAG_STAT_X044); - asm volatile( - " diag 0,0,0x44\n" - "0: la %0,0\n" - "1:\n" - EX_TABLE(0b,1b) - : "=d" (rc) : "0" (-EOPNOTSUPP) : "cc"); - if (!rc) - S390_lowcore.machine_flags |= MACHINE_FLAG_DIAG44; -} - static __init void detect_machine_facilities(void) { if (test_facility(8)) { @@ -331,7 +316,6 @@ void __init startup_init(void) setup_arch_string(); setup_boot_command_line(); detect_diag9c(); - detect_diag44(); detect_machine_facilities(); save_vector_registers(); setup_topology(); diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index 2794cad9312e..a08bd2522dd9 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -413,14 +413,11 @@ EXPORT_SYMBOL(arch_vcpu_is_preempted); void smp_yield_cpu(int cpu) { - if (MACHINE_HAS_DIAG9C) { - diag_stat_inc_norecursion(DIAG_STAT_X09C); - asm volatile("diag %0,0,0x9c" - : : "d" (pcpu_devices[cpu].address)); - } else if (MACHINE_HAS_DIAG44 && !smp_cpu_mtid) { - diag_stat_inc_norecursion(DIAG_STAT_X044); - asm volatile("diag 0,0,0x44"); - } + if (!MACHINE_HAS_DIAG9C) + return; + diag_stat_inc_norecursion(DIAG_STAT_X09C); + asm volatile("diag %0,0,0x9c" + : : "d" (pcpu_devices[cpu].address)); } /* |