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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>
This commit is contained in:
Heiko Carstens 2019-11-29 12:59:59 +01:00 committed by Vasily Gorbik
parent 157309a970
commit 1b68ac8678
3 changed files with 5 additions and 26 deletions
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2
arch/s390/include/asm/setup.h
View File

@ -27,7 +27,6 @@
#define MACHINE_FLAG_DIAG9C BIT(3)
#define MACHINE_FLAG_ESOP BIT(4)
#define MACHINE_FLAG_IDTE BIT(5)
#define MACHINE_FLAG_DIAG44 BIT(6)
#define MACHINE_FLAG_EDAT1 BIT(7)
#define MACHINE_FLAG_EDAT2 BIT(8)
#define MACHINE_FLAG_TOPOLOGY BIT(10)
@ -94,7 +93,6 @@ extern unsigned long __swsusp_reset_dma;
#define MACHINE_HAS_DIAG9C (S390_lowcore.machine_flags & MACHINE_FLAG_DIAG9C)
#define MACHINE_HAS_ESOP (S390_lowcore.machine_flags & MACHINE_FLAG_ESOP)
#define MACHINE_HAS_IDTE (S390_lowcore.machine_flags & MACHINE_FLAG_IDTE)
#define MACHINE_HAS_DIAG44 (S390_lowcore.machine_flags & MACHINE_FLAG_DIAG44)
#define MACHINE_HAS_EDAT1 (S390_lowcore.machine_flags & MACHINE_FLAG_EDAT1)
#define MACHINE_HAS_EDAT2 (S390_lowcore.machine_flags & MACHINE_FLAG_EDAT2)
#define MACHINE_HAS_TOPOLOGY (S390_lowcore.machine_flags & MACHINE_FLAG_TOPOLOGY)

16
arch/s390/kernel/early.c
View File

@ -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();

7
arch/s390/kernel/smp.c
View File

@ -413,14 +413,11 @@ EXPORT_SYMBOL(arch_vcpu_is_preempted);
void smp_yield_cpu(int cpu)
{
if (MACHINE_HAS_DIAG9C) {
if (!MACHINE_HAS_DIAG9C)
return;
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");
}
}
/*