| Message ID | 20220704150514.48816-8-elver@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | perf/hw_breakpoint: Optimize for thousands of tasks | expand |
On Mon, Jul 4, 2022 at 8:06 AM Marco Elver <elver@google.com> wrote: > > 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> > Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Acked-by: Ian Rogers <irogers@google.com> Thanks, Ian > --- > include/linux/hw_breakpoint.h | 1 - > kernel/events/hw_breakpoint.c | 4 +++- > 2 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h > index a3fb846705eb..f319bd26b030 100644 > --- a/include/linux/hw_breakpoint.h > +++ b/include/linux/hw_breakpoint.h > @@ -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); > diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c > index 9fb66d358d81..9c9bf17666a5 100644 > --- a/kernel/events/hw_breakpoint.c > +++ b/kernel/events/hw_breakpoint.c > @@ -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) > { > -- > 2.37.0.rc0.161.g10f37bed90-goog >
diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h index a3fb846705eb..f319bd26b030 100644 --- a/include/linux/hw_breakpoint.h +++ b/include/linux/hw_breakpoint.h @@ -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); diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c index 9fb66d358d81..9c9bf17666a5 100644 --- a/kernel/events/hw_breakpoint.c +++ b/kernel/events/hw_breakpoint.c @@ -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) {
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> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> --- include/linux/hw_breakpoint.h | 1 - kernel/events/hw_breakpoint.c | 4 +++- 2 files changed, 3 insertions(+), 2 deletions(-)