[PATCH] s390 (4/19): micro optimizations.

From: Martin Schwidefsky
Date: Thu Sep 25 2003 - 12:58:03 EST

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- Put cpu number to lowcore.
- Put percpu_offset to lowcore.
- Put current pointer to lowcore.
- Replace barrier() with cpu_relax().

diffstat:
arch/s390/kernel/entry.S | 3 ++-
arch/s390/kernel/entry64.S | 3 ++-
arch/s390/kernel/head.S | 2 ++
arch/s390/kernel/head64.S | 3 +++
arch/s390/kernel/setup.c | 19 +++++++------------
arch/s390/kernel/smp.c | 15 ++++++++++-----
arch/s390/lib/delay.c | 5 +++--
arch/s390/mm/fault.c | 5 ++---
include/asm-s390/current.h | 10 ++--------
include/asm-s390/hardirq.h | 28 +++++++++++++++-------------
include/asm-s390/lowcore.h | 12 ++++++++++--
include/asm-s390/percpu.h | 8 ++++++++
include/asm-s390/smp.h | 2 +-
13 files changed, 67 insertions(+), 48 deletions(-)

diff -urN linux-2.6/arch/s390/kernel/entry.S linux-2.6-s390/arch/s390/kernel/entry.S
--- linux-2.6/arch/s390/kernel/entry.S Thu Sep 25 18:33:22 2003
+++ linux-2.6-s390/arch/s390/kernel/entry.S Thu Sep 25 18:33:24 2003
@@ -141,7 +141,8 @@
stam %a4,%a4,__THREAD_ar4(%r2) # store kernel access reg. 4
lam %a2,%a2,__THREAD_ar2(%r3) # load kernel access reg. 2
lam %a4,%a4,__THREAD_ar4(%r3) # load kernel access reg. 4
- lm %r6,%r15,24(%r15) # load resume registers of next task
+ lm %r6,%r15,24(%r15) # load __switch_to registers of next task
+ st %r3,__LC_CURRENT # __LC_CURRENT = current task struct
l %r3,__THREAD_info(%r3) # load thread_info from task struct
ahi %r3,8192
st %r3,__LC_KERNEL_STACK # __LC_KERNEL_STACK = new kernel stack
diff -urN linux-2.6/arch/s390/kernel/entry64.S linux-2.6-s390/arch/s390/kernel/entry64.S
--- linux-2.6/arch/s390/kernel/entry64.S Thu Sep 25 18:33:22 2003
+++ linux-2.6-s390/arch/s390/kernel/entry64.S Thu Sep 25 18:33:24 2003
@@ -127,7 +127,8 @@
stam %a4,%a4,__THREAD_ar4(%r2) # store kernel access reg. 4
lam %a2,%a2,__THREAD_ar2(%r3) # load kernel access reg. 2
lam %a4,%a4,__THREAD_ar4(%r3) # load kernel access reg. 4
- lmg %r6,%r15,48(%r15) # load resume registers of next task
+ lmg %r6,%r15,48(%r15) # load __switch_to registers of next task
+ stg %r3,__LC_CURRENT # __LC_CURRENT = current task struct
lg %r3,__THREAD_info(%r3) # load thread_info from task struct
aghi %r3,16384
stg %r3,__LC_KERNEL_STACK # __LC_KERNEL_STACK = new kernel stack
diff -urN linux-2.6/arch/s390/kernel/head.S linux-2.6-s390/arch/s390/kernel/head.S
--- linux-2.6/arch/s390/kernel/head.S Mon Sep 8 21:49:58 2003
+++ linux-2.6-s390/arch/s390/kernel/head.S Thu Sep 25 18:33:24 2003
@@ -30,6 +30,7 @@
#include <linux/config.h>
#include <asm/setup.h>
#include <asm/lowcore.h>
+#include <asm/offsets.h>

#ifndef CONFIG_IPL
.org 0
@@ -633,6 +634,7 @@
# Setup stack
#
l %r15,.Linittu-.LPG2(%r13)
+ mvc __LC_CURRENT(4),__TI_task(%r15)
ahi %r15,8192 # init_task_union + 8192
st %r15,__LC_KERNEL_STACK # set end of kernel stack
ahi %r15,-96
diff -urN linux-2.6/arch/s390/kernel/head64.S linux-2.6-s390/arch/s390/kernel/head64.S
--- linux-2.6/arch/s390/kernel/head64.S Mon Sep 8 21:50:01 2003
+++ linux-2.6-s390/arch/s390/kernel/head64.S Thu Sep 25 18:33:24 2003
@@ -30,6 +30,7 @@
#include <linux/config.h>
#include <asm/setup.h>
#include <asm/lowcore.h>
+#include <asm/offsets.h>

#ifndef CONFIG_IPL
.org 0
@@ -642,6 +643,8 @@
# Setup stack
#
larl %r15,init_thread_union
+ lg %r14,__TI_task(%r15) # cache current in lowcore
+ stg %r14,__LC_CURRENT
aghi %r15,16384 # init_task_union + 16384
stg %r15,__LC_KERNEL_STACK # set end of kernel stack
aghi %r15,-160
diff -urN linux-2.6/arch/s390/kernel/setup.c linux-2.6-s390/arch/s390/kernel/setup.c
--- linux-2.6/arch/s390/kernel/setup.c Mon Sep 8 21:49:52 2003
+++ linux-2.6-s390/arch/s390/kernel/setup.c Thu Sep 25 18:33:24 2003
@@ -97,7 +97,6 @@
*/
asm volatile ("stidp %0": "=m" (S390_lowcore.cpu_data.cpu_id));
S390_lowcore.cpu_data.cpu_addr = addr;
- S390_lowcore.cpu_data.cpu_nr = nr;

/*
* Force FPU initialization:
@@ -418,7 +417,7 @@
* we are rounding upwards:
*/
start_pfn = (__pa(&_end) + PAGE_SIZE - 1) >> PAGE_SHIFT;
- end_pfn = memory_end >> PAGE_SHIFT;
+ end_pfn = max_pfn = memory_end >> PAGE_SHIFT;

/*
* Initialize the boot-time allocator (with low memory only):
@@ -497,21 +496,17 @@
lc->io_new_psw.addr = PSW_ADDR_AMODE + (unsigned long) io_int_handler;
lc->ipl_device = S390_lowcore.ipl_device;
lc->jiffy_timer = -1LL;
-#ifndef CONFIG_ARCH_S390X
- lc->kernel_stack = ((__u32) &init_thread_union) + 8192;
- lc->async_stack = (__u32)
- __alloc_bootmem(2*PAGE_SIZE, 2*PAGE_SIZE, 0) + 8192;
- set_prefix((__u32) lc);
-#else /* CONFIG_ARCH_S390X */
- lc->kernel_stack = ((__u64) &init_thread_union) + 16384;
- lc->async_stack = (__u64)
- __alloc_bootmem(4*PAGE_SIZE, 4*PAGE_SIZE, 0) + 16384;
+ lc->kernel_stack = ((unsigned long) &init_thread_union) + THREAD_SIZE;
+ lc->async_stack = (unsigned long)
+ __alloc_bootmem(ASYNC_SIZE, ASYNC_SIZE, 0) + ASYNC_SIZE;
+ lc->current_task = (unsigned long) init_thread_union.thread_info.task;
+#ifdef CONFIG_ARCH_S390X
if (MACHINE_HAS_DIAG44)
lc->diag44_opcode = 0x83000044;
else
lc->diag44_opcode = 0x07000700;
- set_prefix((__u32)(__u64) lc);
#endif /* CONFIG_ARCH_S390X */
+ set_prefix((u32)(unsigned long) lc);
cpu_init();
__cpu_logical_map[0] = S390_lowcore.cpu_data.cpu_addr;

diff -urN linux-2.6/arch/s390/kernel/smp.c linux-2.6-s390/arch/s390/kernel/smp.c
--- linux-2.6/arch/s390/kernel/smp.c Thu Sep 25 18:33:22 2003
+++ linux-2.6-s390/arch/s390/kernel/smp.c Thu Sep 25 18:33:24 2003
@@ -138,11 +138,11 @@

/* Wait for response */
while (atomic_read(&data.started) != cpus)
- barrier();
+ cpu_relax();

if (wait)
while (atomic_read(&data.finished) != cpus)
- barrier();
+ cpu_relax();
spin_unlock(&call_lock);

return 0;
@@ -207,7 +207,8 @@
cpu_clear(smp_processor_id(), cpu_restart_map);
if (smp_processor_id() == 0) {
/* Wait for all other cpus to enter do_machine_restart. */
- while (!cpus_empty(cpu_restart_map));
+ while (!cpus_empty(cpu_restart_map))
+ cpu_relax();
/* Store status of other cpus. */
do_store_status();
/*
@@ -524,8 +525,11 @@
__asm__ __volatile__("stam 0,15,0(%0)"
: : "a" (&cpu_lowcore->access_regs_save_area)
: "memory");
- eieio();
- signal_processor(cpu,sigp_restart);
+ cpu_lowcore->percpu_offset = __per_cpu_offset[cpu];
+ cpu_lowcore->current_task = (unsigned long) idle;
+ cpu_lowcore->cpu_data.cpu_nr = cpu;
+ eieio();
+ signal_processor(cpu,sigp_restart);

while (!cpu_online(cpu));
return 0;
@@ -570,6 +574,7 @@
{
cpu_set(smp_processor_id(), cpu_online_map);
cpu_set(smp_processor_id(), cpu_possible_map);
+ S390_lowcore.percpu_offset = __per_cpu_offset[smp_processor_id()];
}

void smp_cpus_done(unsigned int max_cpus)
diff -urN linux-2.6/arch/s390/lib/delay.c linux-2.6-s390/arch/s390/lib/delay.c
--- linux-2.6/arch/s390/lib/delay.c Mon Sep 8 21:49:59 2003
+++ linux-2.6-s390/arch/s390/lib/delay.c Thu Sep 25 18:33:24 2003
@@ -34,7 +34,8 @@
}

/*
- * Waits for 'usecs' microseconds using the tod clock
+ * Waits for 'usecs' microseconds using the tod clock, giving up the time slice
+ * of the virtual PU inbetween to avoid congestion.
*/
void __udelay(unsigned long usecs)
{
@@ -44,7 +45,7 @@
return;
asm volatile ("STCK %0" : "=m" (start_cc));
do {
+ cpu_relax();
asm volatile ("STCK %0" : "=m" (end_cc));
} while (((end_cc - start_cc)/4096) < usecs);
}
-
diff -urN linux-2.6/arch/s390/mm/fault.c linux-2.6-s390/arch/s390/mm/fault.c
--- linux-2.6/arch/s390/mm/fault.c Mon Sep 8 21:50:21 2003
+++ linux-2.6-s390/arch/s390/mm/fault.c Thu Sep 25 18:33:24 2003
@@ -488,7 +488,7 @@
int pfault_init(void)
{
pfault_refbk_t refbk =
- { 0x258, 0, 5, 2, __LC_KERNEL_STACK, 1ULL << 48, 1ULL << 48,
+ { 0x258, 0, 5, 2, __LC_CURRENT, 1ULL << 48, 1ULL << 48,
__PF_RES_FIELD };
int rc;

@@ -555,8 +555,7 @@
/*
* Get the token (= address of kernel stack of affected task).
*/
- tsk = (struct task_struct *)
- (*((unsigned long *) __LC_PFAULT_INTPARM) - THREAD_SIZE);
+ tsk = *(struct task_struct **) __LC_PFAULT_INTPARM;

/*
* We got all needed information from the lowcore and can
diff -urN linux-2.6/include/asm-s390/current.h linux-2.6-s390/include/asm-s390/current.h
--- linux-2.6/include/asm-s390/current.h Mon Sep 8 21:50:32 2003
+++ linux-2.6-s390/include/asm-s390/current.h Thu Sep 25 18:33:24 2003
@@ -12,17 +12,11 @@
#define _S390_CURRENT_H

#ifdef __KERNEL__
-
-#include <linux/thread_info.h>
+#include <asm/lowcore.h>

struct task_struct;

-static inline struct task_struct * get_current(void)
-{
- return current_thread_info()->task;
-}
-
-#define current get_current()
+#define current ((struct task_struct *const)S390_lowcore.current_task)

#endif

diff -urN linux-2.6/include/asm-s390/hardirq.h linux-2.6-s390/include/asm-s390/hardirq.h
--- linux-2.6/include/asm-s390/hardirq.h Mon Sep 8 21:50:43 2003
+++ linux-2.6-s390/include/asm-s390/hardirq.h Thu Sep 25 18:33:24 2003
@@ -18,14 +18,17 @@
#include <linux/cache.h>
#include <asm/lowcore.h>

-/* entry.S is sensitive to the offsets of these fields */
+/* irq_cpustat_t is unused currently, but could be converted
+ * into a percpu variable instead of storing softirq_pending
+ * on the lowcore */
typedef struct {
unsigned int __softirq_pending;
- unsigned int __syscall_count;
- struct task_struct * __ksoftirqd_task; /* waitqueue is too large */
-} ____cacheline_aligned irq_cpustat_t;
+} irq_cpustat_t;

-#include <linux/irq_cpustat.h> /* Standard mappings for irq_cpustat_t above */
+#define softirq_pending(cpu) (lowcore_ptr[(cpu)]->softirq_pending)
+#define local_softirq_pending() (S390_lowcore.softirq_pending)
+
+#define __ARCH_IRQ_STAT

/*
* We put the hardirq and softirq counter into the preemption
@@ -76,7 +79,12 @@
#define hardirq_trylock() (!in_interrupt())
#define hardirq_endlock() do { } while (0)

-#define irq_enter() (preempt_count() += HARDIRQ_OFFSET)
+#define irq_enter() \
+do { \
+ BUG_ON( hardirq_count() ); \
+ (preempt_count() += HARDIRQ_OFFSET); \
+} while(0)
+

extern void do_call_softirq(void);

@@ -93,16 +101,10 @@
#define irq_exit() \
do { \
preempt_count() -= IRQ_EXIT_OFFSET; \
- if (!in_interrupt() && softirq_pending(smp_processor_id())) \
+ if (!in_interrupt() && local_softirq_pending()) \
/* Use the async. stack for softirq */ \
do_call_softirq(); \
preempt_enable_no_resched(); \
} while (0)

-#ifndef CONFIG_SMP
-# define synchronize_irq(irq) barrier()
-#else
- extern void synchronize_irq(unsigned int irq);
-#endif /* CONFIG_SMP */
-
#endif /* __ASM_HARDIRQ_H */
diff -urN linux-2.6/include/asm-s390/lowcore.h linux-2.6-s390/include/asm-s390/lowcore.h
--- linux-2.6/include/asm-s390/lowcore.h Mon Sep 8 21:50:04 2003
+++ linux-2.6-s390/include/asm-s390/lowcore.h Thu Sep 25 18:33:24 2003
@@ -65,6 +65,7 @@
#define __LC_CPUADDR 0xC68
#define __LC_IPLDEV 0xC7C
#define __LC_JIFFY_TIMER 0xC80
+#define __LC_CURRENT 0xC90
#else /* __s390x__ */
#define __LC_KERNEL_STACK 0xD40
#define __LC_ASYNC_STACK 0xD48
@@ -72,6 +73,7 @@
#define __LC_CPUADDR 0xD98
#define __LC_IPLDEV 0xDB8
#define __LC_JIFFY_TIMER 0xDC0
+#define __LC_CURRENT 0xDD8
#endif /* __s390x__ */

#define __LC_PANIC_MAGIC 0xE00
@@ -169,7 +171,10 @@
/* SMP info area: defined by DJB */
__u64 jiffy_timer; /* 0xc80 */
__u32 ext_call_fast; /* 0xc88 */
- __u8 pad11[0xe00-0xc8c]; /* 0xc8c */
+ __u32 percpu_offset; /* 0xc8c */
+ __u32 current_task; /* 0xc90 */
+ __u32 softirq_pending; /* 0xc94 */
+ __u8 pad11[0xe00-0xc98]; /* 0xc98 */

/* 0xe00 is used as indicator for dump tools */
/* whether the kernel died with panic() or not */
@@ -244,7 +249,10 @@
/* SMP info area: defined by DJB */
__u64 jiffy_timer; /* 0xdc0 */
__u64 ext_call_fast; /* 0xdc8 */
- __u8 pad12[0xe00-0xdd0]; /* 0xdd0 */
+ __u64 percpu_offset; /* 0xdd0 */
+ __u64 current_task; /* 0xdd8 */
+ __u64 softirq_pending; /* 0xde0 */
+ __u8 pad12[0xe00-0xde8]; /* 0xde8 */

/* 0xe00 is used as indicator for dump tools */
/* whether the kernel died with panic() or not */
diff -urN linux-2.6/include/asm-s390/percpu.h linux-2.6-s390/include/asm-s390/percpu.h
--- linux-2.6/include/asm-s390/percpu.h Mon Sep 8 21:50:32 2003
+++ linux-2.6-s390/include/asm-s390/percpu.h Thu Sep 25 18:33:24 2003
@@ -2,5 +2,13 @@
#define __ARCH_S390_PERCPU__

#include <asm-generic/percpu.h>
+#include <asm/lowcore.h>
+
+/*
+ * s390 uses the generic implementation for per cpu data, with the exception that
+ * the offset of the cpu local data area is cached in the cpu's lowcore memory
+ */
+#undef __get_cpu_var
+#define __get_cpu_var(var) (*RELOC_HIDE(&per_cpu__##var, S390_lowcore.percpu_offset))

#endif /* __ARCH_S390_PERCPU__ */
diff -urN linux-2.6/include/asm-s390/smp.h linux-2.6-s390/include/asm-s390/smp.h
--- linux-2.6/include/asm-s390/smp.h Mon Sep 8 21:50:06 2003
+++ linux-2.6-s390/include/asm-s390/smp.h Thu Sep 25 18:33:24 2003
@@ -46,7 +46,7 @@

#define PROC_CHANGE_PENALTY 20 /* Schedule penalty */

-#define smp_processor_id() (current_thread_info()->cpu)
+#define smp_processor_id() (S390_lowcore.cpu_data.cpu_nr)

#define cpu_online(cpu) cpu_isset(cpu, cpu_online_map)
#define cpu_possible(cpu) cpu_isset(cpu, cpu_possible_map)
-
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