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perf/hw_breakpoint: Make hw_breakpoint_weight() inlinable

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Due to being a __weak function, hw_breakpoint_weight() will cause the
compiler to always emit a call to it. This generates unnecessarily bad
code (register spills etc.) for no good reason; in fact it appears in
profiles of `perf bench -r 100 breakpoint thread -b 4 -p 128 -t 512`:

    ...
    0.70%  [kernel]       [k] hw_breakpoint_weight
    ...

While a small percentage, no architecture defines its own
hw_breakpoint_weight() nor are there users outside hw_breakpoint.c,
which makes the fact it is currently __weak a poor choice.

Change hw_breakpoint_weight()'s definition to follow a similar protocol
to hw_breakpoint_slots(), such that if <asm/hw_breakpoint.h> defines
hw_breakpoint_weight(), we'll use it instead.

The result is that it is inlined and no longer shows up in profiles.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20220829124719.675715-8-elver@google.com
This commit is contained in:
Marco Elver 2022-08-29 14:47:12 +02:00 committed by Peter Zijlstra
parent be3f152568
commit 9caf87be11
2 changed files with 3 additions and 2 deletions
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1
include/linux/hw_breakpoint.h
View File

@ -80,7 +80,6 @@ extern int dbg_reserve_bp_slot(struct perf_event *bp);
extern int dbg_release_bp_slot(struct perf_event *bp);
extern int reserve_bp_slot(struct perf_event *bp);
extern void release_bp_slot(struct perf_event *bp);
int hw_breakpoint_weight(struct perf_event *bp);
int arch_reserve_bp_slot(struct perf_event *bp);
void arch_release_bp_slot(struct perf_event *bp);
void arch_unregister_hw_breakpoint(struct perf_event *bp);

4
kernel/events/hw_breakpoint.c
View File

@ -124,10 +124,12 @@ static __init int init_breakpoint_slots(void)
}
#endif
__weak int hw_breakpoint_weight(struct perf_event *bp)
#ifndef hw_breakpoint_weight
static inline int hw_breakpoint_weight(struct perf_event *bp)
{
return 1;
}
#endif
static inline enum bp_type_idx find_slot_idx(u64 bp_type)
{