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s390/preempt: move preempt_count to the lowcore

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Convert s390 to use a field in the struct lowcore for the CPU
preemption count. It is a bit cheaper to access a lowcore field
compared to a thread_info variable and it removes the depencency
on a task related structure.

bloat-o-meter on the vmlinux image for the default configuration
(CONFIG_PREEMPT_NONE=y) reports a small reduction in text size:

add/remove: 0/0 grow/shrink: 18/578 up/down: 228/-5448 (-5220)

A larger improvement is achieved with the default configuration
but with CONFIG_PREEMPT=y and CONFIG_DEBUG_PREEMPT=n:

add/remove: 2/6 grow/shrink: 59/4477 up/down: 1618/-228762 (-227144)

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
2016-10-25 12:21:44 +02:00
parent 1993dbc7e0
commit c360192bf4
8 changed files with 144 additions and 5 deletions
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2
arch/s390/include/asm/thread_info.h
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@@ -34,7 +34,6 @@ struct thread_info {
unsigned long flags; /* low level flags */
unsigned long sys_call_table; /* System call table address */
unsigned int cpu; /* current CPU */
int preempt_count; /* 0 => preemptable, <0 => BUG */
unsigned int system_call;
__u64 user_timer;
__u64 system_timer;
@@ -49,7 +48,6 @@ struct thread_info {
.task = &tsk, \
.flags = 0, \
.cpu = 0, \
.preempt_count = INIT_PREEMPT_COUNT, \
}
#define init_thread_info (init_thread_union.thread_info)