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 <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>

Author: heicarst

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)

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();

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));
 }
 
 /*