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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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3
arch/s390/include/asm/lowcore.h
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@@ -126,7 +126,8 @@ struct lowcore {
__u64 percpu_offset; /* 0x0378 */
__u64 vdso_per_cpu_data; /* 0x0380 */
__u64 machine_flags; /* 0x0388 */
__u8 pad_0x0390[0x0398-0x0390]; /* 0x0390 */
__u32 preempt_count; /* 0x0390 */
__u8 pad_0x0394[0x0398-0x0394]; /* 0x0394 */
__u64 gmap; /* 0x0398 */
__u32 spinlock_lockval; /* 0x03a0 */
__u32 fpu_flags; /* 0x03a4 */