Messages in this thread | | | From | Dmitry Vyukov <> | Date | Thu, 9 Jun 2022 15:41:26 +0200 | Subject | Re: [PATCH 5/8] perf/hw_breakpoint: Remove useless code related to flexible breakpoints |
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On Thu, 9 Jun 2022 at 14:04, Dmitry Vyukov <dvyukov@google.com> wrote: > > On Thu, 9 Jun 2022 at 13:31, Marco Elver <elver@google.com> wrote: > > > > Flexible breakpoints have never been implemented, with > > bp_cpuinfo::flexible always being 0. Unfortunately, they still occupy 4 > > bytes in each bp_cpuinfo and bp_busy_slots, as well as computing the max > > flexible count in fetch_bp_busy_slots(). > > > > This again causes suboptimal code generation, when we always know that > > `!!slots.flexible` will be 0. > > > > Just get rid of the flexible "placeholder" and remove all real code > > related to it. Make a note in the comment related to the constraints > > algorithm but don't remove them from the algorithm, so that if in future > > flexible breakpoints need supporting, it should be trivial to revive > > them (along with reverting this change). > > > > Signed-off-by: Marco Elver <elver@google.com> > > Was added in 2009. > > Acked-by: Dmitry Vyukov <dvyukov@google.com> > > > --- > > kernel/events/hw_breakpoint.c | 12 +++--------- > > 1 file changed, 3 insertions(+), 9 deletions(-) > > > > diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c > > index 5f40c8dfa042..afe0a6007e96 100644 > > --- a/kernel/events/hw_breakpoint.c > > +++ b/kernel/events/hw_breakpoint.c > > @@ -46,8 +46,6 @@ struct bp_cpuinfo { > > #else > > unsigned int *tsk_pinned; > > #endif > > - /* Number of non-pinned cpu/task breakpoints in a cpu */ > > - unsigned int flexible; /* XXX: placeholder, see fetch_this_slot() */ > > }; > > > > static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]); > > @@ -71,7 +69,6 @@ static bool constraints_initialized __ro_after_init; > > /* Gather the number of total pinned and un-pinned bp in a cpuset */ > > struct bp_busy_slots {
Do we also want to remove this struct altogether? Now it becomes just an int counter.
> > unsigned int pinned; > > - unsigned int flexible; > > }; > > > > /* Serialize accesses to the above constraints */ > > @@ -213,10 +210,6 @@ fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp, > > > > if (nr > slots->pinned) > > slots->pinned = nr; > > - > > - nr = info->flexible; > > - if (nr > slots->flexible) > > - slots->flexible = nr; > > } > > } > > > > @@ -299,7 +292,8 @@ __weak void arch_unregister_hw_breakpoint(struct perf_event *bp) > > } > > > > /* > > - * Constraints to check before allowing this new breakpoint counter: > > + * Constraints to check before allowing this new breakpoint counter. Note that > > + * flexible breakpoints are currently unsupported -- see fetch_this_slot(). > > * > > * == Non-pinned counter == (Considered as pinned for now) > > * > > @@ -366,7 +360,7 @@ static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type) > > fetch_this_slot(&slots, weight); > > > > /* Flexible counters need to keep at least one slot */ > > - if (slots.pinned + (!!slots.flexible) > hw_breakpoint_slots_cached(type)) > > + if (slots.pinned > hw_breakpoint_slots_cached(type)) > > return -ENOSPC; > > > > ret = arch_reserve_bp_slot(bp); > > -- > > 2.36.1.255.ge46751e96f-goog > >
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