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powerpc/pseries: Use jump labels for hcall tracepoints

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hcall tracepoints add quite a few instructions to our hcall path:

plpar_hcall:
	mr      r2,r2
	mfcr    r0
	stw     r0,8(r1)
	b       164		<---- start
	ld      r12,0(r2)
	std     r12,32(r1)
	cmpdi   r12,0
	beq     164		<---- end
...

We have an unconditional branch that gets noped out during boot and
a load/compare/branch. We also store the tracepoint value to the
stack for the hcall_exit path to use.

By using jump labels we can simplify this to just a single nop that
gets replaced with a branch when the tracepoint is enabled:

plpar_hcall:
	mr      r2,r2
	mfcr    r0
	stw     r0,8(r1)
	nop			<----
...

If jump labels are not enabled, we fall back to the old method.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard
2014-07-03 15:52:03 +10:00
committed by Benjamin Herrenschmidt
parent 8fa5d4547e
commit cc1adb5f32
3 changed files with 142 additions and 41 deletions
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30
arch/powerpc/platforms/pseries/lpar.c
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@@ -26,6 +26,7 @@
#include <linux/dma-mapping.h>
#include <linux/console.h>
#include <linux/export.h>
#include <linux/static_key.h>
#include <asm/processor.h>
#include <asm/mmu.h>
#include <asm/page.h>
@@ -649,6 +650,19 @@ EXPORT_SYMBOL(arch_free_page);
#endif
#ifdef CONFIG_TRACEPOINTS
#ifdef CONFIG_JUMP_LABEL
struct static_key hcall_tracepoint_key = STATIC_KEY_INIT;
void hcall_tracepoint_regfunc(void)
{
static_key_slow_inc(&hcall_tracepoint_key);
}
void hcall_tracepoint_unregfunc(void)
{
static_key_slow_dec(&hcall_tracepoint_key);
}
#else
/*
* We optimise our hcall path by placing hcall_tracepoint_refcount
* directly in the TOC so we can check if the hcall tracepoints are
@@ -658,13 +672,6 @@ EXPORT_SYMBOL(arch_free_page);
/* NB: reg/unreg are called while guarded with the tracepoints_mutex */
extern long hcall_tracepoint_refcount;
/*
* Since the tracing code might execute hcalls we need to guard against
* recursion. One example of this are spinlocks calling H_YIELD on
* shared processor partitions.
*/
static DEFINE_PER_CPU(unsigned int, hcall_trace_depth);
void hcall_tracepoint_regfunc(void)
{
hcall_tracepoint_refcount++;
@@ -674,6 +681,15 @@ void hcall_tracepoint_unregfunc(void)
{
hcall_tracepoint_refcount--;
}
#endif
/*
* Since the tracing code might execute hcalls we need to guard against
* recursion. One example of this are spinlocks calling H_YIELD on
* shared processor partitions.
*/
static DEFINE_PER_CPU(unsigned int, hcall_trace_depth);
void __trace_hcall_entry(unsigned long opcode, unsigned long *args)
{