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s390/ftrace: optimize function graph caller code

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When the function graph tracer is disabled we can skip three additional
instructions. So let's just do this.

So if function tracing is enabled but function graph tracing is
runtime disabled, we get away with a single unconditional branch.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Heiko Carstens 2014-08-15 12:33:46 +02:00 committed by Martin Schwidefsky
parent 0f1b1ff54b
commit 2481a87b02
3 changed files with 34 additions and 6 deletions
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1
arch/s390/include/asm/ftrace.h
View File

@ -4,6 +4,7 @@
#ifndef __ASSEMBLY__
extern void _mcount(void);
extern char ftrace_graph_caller_end;
struct dyn_arch_ftrace { };

24
arch/s390/kernel/ftrace.c
View File

@ -170,6 +170,29 @@ out:
* directly after the instructions. To enable the call we calculate
* the original offset to prepare_ftrace_return and put it back.
*/
#ifdef CONFIG_64BIT
int ftrace_enable_ftrace_graph_caller(void)
{
static unsigned short offset = 0x0002;
return probe_kernel_write((void *) ftrace_graph_caller + 2,
&offset, sizeof(offset));
}
int ftrace_disable_ftrace_graph_caller(void)
{
unsigned short offset;
offset = ((void *) &ftrace_graph_caller_end -
(void *) ftrace_graph_caller) / 2;
return probe_kernel_write((void *) ftrace_graph_caller + 2,
&offset, sizeof(offset));
}
#else /* CONFIG_64BIT */
int ftrace_enable_ftrace_graph_caller(void)
{
unsigned short offset;
@ -188,5 +211,6 @@ int ftrace_disable_ftrace_graph_caller(void)
&offset, sizeof(offset));
}
#endif /* CONFIG_64BIT */
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

15
arch/s390/kernel/mcount64.S
View File

@ -32,14 +32,17 @@ ENTRY(ftrace_caller)
lg %r14,0(%r14)
basr %r14,%r14
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
# The j instruction gets runtime patched to a nop instruction.
# See ftrace_enable_ftrace_graph_caller. The patched instruction is:
# j .+4
ENTRY(ftrace_graph_caller)
j ftrace_graph_caller_end
lg %r2,168(%r15)
lg %r3,272(%r15)
ENTRY(ftrace_graph_caller)
# The bras instruction gets runtime patched to call prepare_ftrace_return.
# See ftrace_enable_ftrace_graph_caller. The patched instruction is:
# bras %r14,prepare_ftrace_return
bras %r14,0f
0: stg %r2,168(%r15)
brasl %r14,prepare_ftrace_return
stg %r2,168(%r15)
ftrace_graph_caller_end:
.globl ftrace_graph_caller_end
#endif
aghi %r15,160
lmg %r2,%r5,32(%r15)