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>

diff --git a/arch/s390/include/asm/setup.h b/arch/s390/include/asm/setup.h
index 6dc6c4f..69289e9 100644 (file)
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -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)

diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index db32a55..cd241ee 100644 (file)
--- 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 2794cad..a08bd25 100644 (file)
--- 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));
 }
 
 /*