Messages in this thread | | | Date | Wed, 21 Apr 2010 10:32:54 +0200 | Subject | Re: [RFC] perf_events: support for uncore a.k.a. nest units | From | stephane eranian <> |
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Seems to me that struct pmu is a shared resource across all CPUs. I don't understand why scheduling on one CPU would have to impact all the other CPUs, unless I am missing something here.
On Wed, Apr 21, 2010 at 10:08 AM, Lin Ming <ming.m.lin@intel.com> wrote: > On Tue, 2010-04-20 at 20:03 +0800, Peter Zijlstra wrote: >> On Tue, 2010-04-20 at 19:55 +0800, Lin Ming wrote: >> >> > > One thing not on that list, which should happen first I guess, is to >> > > remove hw_perf_group_sched_in(). The idea is to add some sort of >> > > transactional API to the struct pmu, so that we can delay the >> > > schedulability check until commit time (and roll back when it fails). >> > > >> > > Something as simple as: >> > > >> > > struct pmu { >> > > void start_txn(struct pmu *); >> > > void commit_txn(struct pmu *); >> > > >> > > ,,, >> > > }; >> > >> > Could you please explain a bit more? >> > >> > Does it mean that "start_txn" perform the schedule events stuff >> > and "commit_txn" perform the assign events stuff? >> > >> > Does "commit time" mean the actual activation in hw_perf_enable? >> >> No, the idea behind hw_perf_group_sched_in() is to not perform >> schedulability tests on each event in the group, but to add the group as >> a whole and then perform one test. >> >> Of course, when that test fails, you'll have to roll-back the whole >> group again. >> >> So start_txn (or a better name) would simply toggle a flag in the pmu >> implementation that will make pmu::enable() not perform the >> schedulablilty test. >> >> Then commit_txn() will perform the schedulability test (so note the >> method has to have a !void return value, my mistake in the earlier >> email). >> >> This will allow us to use the regular >> kernel/perf_event.c::group_sched_in() and all the rollback code. >> Currently each hw_perf_group_sched_in() implementation duplicates all >> the rolllback code (with various bugs). >> >> >> >> We must get rid of all weak hw_perf_*() functions before we can properly >> consider multiple struct pmu implementations. >> > > Thanks for the clear explanation. > > Does below patch show what you mean? > > I only touch the x86 arch code now. > > --- > arch/x86/kernel/cpu/perf_event.c | 161 +++++++++++-------------------------- > include/linux/perf_event.h | 10 ++- > kernel/perf_event.c | 28 +++---- > 3 files changed, 67 insertions(+), 132 deletions(-) > > diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c > index 626154a..62aa9a1 100644 > --- a/arch/x86/kernel/cpu/perf_event.c > +++ b/arch/x86/kernel/cpu/perf_event.c > @@ -944,6 +944,9 @@ static int x86_pmu_enable(struct perf_event *event) > if (n < 0) > return n; > > + if (!(event->pmu->flag & PERF_EVENT_TRAN_STARTED)) > + goto out; > + > ret = x86_pmu.schedule_events(cpuc, n, assign); > if (ret) > return ret; > @@ -953,6 +956,7 @@ static int x86_pmu_enable(struct perf_event *event) > */ > memcpy(cpuc->assign, assign, n*sizeof(int)); > > +out: > cpuc->n_events = n; > cpuc->n_added += n - n0; > > @@ -1210,119 +1214,6 @@ x86_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event) > return &unconstrained; > } > > -static int x86_event_sched_in(struct perf_event *event, > - struct perf_cpu_context *cpuctx) > -{ > - int ret = 0; > - > - event->state = PERF_EVENT_STATE_ACTIVE; > - event->oncpu = smp_processor_id(); > - event->tstamp_running += event->ctx->time - event->tstamp_stopped; > - > - if (!is_x86_event(event)) > - ret = event->pmu->enable(event); > - > - if (!ret && !is_software_event(event)) > - cpuctx->active_oncpu++; > - > - if (!ret && event->attr.exclusive) > - cpuctx->exclusive = 1; > - > - return ret; > -} > - > -static void x86_event_sched_out(struct perf_event *event, > - struct perf_cpu_context *cpuctx) > -{ > - event->state = PERF_EVENT_STATE_INACTIVE; > - event->oncpu = -1; > - > - if (!is_x86_event(event)) > - event->pmu->disable(event); > - > - event->tstamp_running -= event->ctx->time - event->tstamp_stopped; > - > - if (!is_software_event(event)) > - cpuctx->active_oncpu--; > - > - if (event->attr.exclusive || !cpuctx->active_oncpu) > - cpuctx->exclusive = 0; > -} > - > -/* > - * Called to enable a whole group of events. > - * Returns 1 if the group was enabled, or -EAGAIN if it could not be. > - * Assumes the caller has disabled interrupts and has > - * frozen the PMU with hw_perf_save_disable. > - * > - * called with PMU disabled. If successful and return value 1, > - * then guaranteed to call perf_enable() and hw_perf_enable() > - */ > -int hw_perf_group_sched_in(struct perf_event *leader, > - struct perf_cpu_context *cpuctx, > - struct perf_event_context *ctx) > -{ > - struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events); > - struct perf_event *sub; > - int assign[X86_PMC_IDX_MAX]; > - int n0, n1, ret; > - > - if (!x86_pmu_initialized()) > - return 0; > - > - /* n0 = total number of events */ > - n0 = collect_events(cpuc, leader, true); > - if (n0 < 0) > - return n0; > - > - ret = x86_pmu.schedule_events(cpuc, n0, assign); > - if (ret) > - return ret; > - > - ret = x86_event_sched_in(leader, cpuctx); > - if (ret) > - return ret; > - > - n1 = 1; > - list_for_each_entry(sub, &leader->sibling_list, group_entry) { > - if (sub->state > PERF_EVENT_STATE_OFF) { > - ret = x86_event_sched_in(sub, cpuctx); > - if (ret) > - goto undo; > - ++n1; > - } > - } > - /* > - * copy new assignment, now we know it is possible > - * will be used by hw_perf_enable() > - */ > - memcpy(cpuc->assign, assign, n0*sizeof(int)); > - > - cpuc->n_events = n0; > - cpuc->n_added += n1; > - ctx->nr_active += n1; > - > - /* > - * 1 means successful and events are active > - * This is not quite true because we defer > - * actual activation until hw_perf_enable() but > - * this way we* ensure caller won't try to enable > - * individual events > - */ > - return 1; > -undo: > - x86_event_sched_out(leader, cpuctx); > - n0 = 1; > - list_for_each_entry(sub, &leader->sibling_list, group_entry) { > - if (sub->state == PERF_EVENT_STATE_ACTIVE) { > - x86_event_sched_out(sub, cpuctx); > - if (++n0 == n1) > - break; > - } > - } > - return ret; > -} > - > #include "perf_event_amd.c" > #include "perf_event_p6.c" > #include "perf_event_p4.c" > @@ -1454,6 +1345,47 @@ static inline void x86_pmu_read(struct perf_event *event) > x86_perf_event_update(event); > } > > +/* > + * Set the flag to make pmu::enable() not perform the > + * schedulablilty test. > + */ > +static void x86_pmu_start_txn(struct pmu *pmu) > +{ > + pmu->flag |= PERF_EVENT_TRAN_STARTED; > +} > + > +static void x86_pmu_stop_txn(struct pmu *pmu) > +{ > + pmu->flag &= ~PERF_EVENT_TRAN_STARTED; > +} > + > +/* > + * Return 0 if commit transaction success > + */ > +static int x86_pmu_commit_txn(struct pmu *pmu) > +{ > + struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events); > + int assign[X86_PMC_IDX_MAX]; > + int n, ret; > + > + n = cpuc->n_events; > + > + if (!x86_pmu_initialized()) > + return -EAGAIN; > + > + ret = x86_pmu.schedule_events(cpuc, n, assign); > + if (ret) > + return ret; > + > + /* > + * copy new assignment, now we know it is possible > + * will be used by hw_perf_enable() > + */ > + memcpy(cpuc->assign, assign, n*sizeof(int)); > + > + return 0; > +} > + > static const struct pmu pmu = { > .enable = x86_pmu_enable, > .disable = x86_pmu_disable, > @@ -1461,6 +1393,9 @@ static const struct pmu pmu = { > .stop = x86_pmu_stop, > .read = x86_pmu_read, > .unthrottle = x86_pmu_unthrottle, > + .start_txn = x86_pmu_start_txn, > + .stop_txn = x86_pmu_stop_txn, > + .commit_txn = x86_pmu_commit_txn, > }; > > /* > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index bf896d0..93aa8d8 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -524,6 +524,8 @@ struct hw_perf_event { > > struct perf_event; > > +#define PERF_EVENT_TRAN_STARTED 1 > + > /** > * struct pmu - generic performance monitoring unit > */ > @@ -534,6 +536,11 @@ struct pmu { > void (*stop) (struct perf_event *event); > void (*read) (struct perf_event *event); > void (*unthrottle) (struct perf_event *event); > + void (*start_txn) (struct pmu *pmu); > + void (*stop_txn) (struct pmu *pmu); > + int (*commit_txn) (struct pmu *pmu); > + > + u8 flag; > }; > > /** > @@ -799,9 +806,6 @@ extern void perf_disable(void); > extern void perf_enable(void); > extern int perf_event_task_disable(void); > extern int perf_event_task_enable(void); > -extern int hw_perf_group_sched_in(struct perf_event *group_leader, > - struct perf_cpu_context *cpuctx, > - struct perf_event_context *ctx); > extern void perf_event_update_userpage(struct perf_event *event); > extern int perf_event_release_kernel(struct perf_event *event); > extern struct perf_event * > diff --git a/kernel/perf_event.c b/kernel/perf_event.c > index 07b7a43..4537676 100644 > --- a/kernel/perf_event.c > +++ b/kernel/perf_event.c > @@ -83,14 +83,6 @@ extern __weak const struct pmu *hw_perf_event_init(struct perf_event *event) > void __weak hw_perf_disable(void) { barrier(); } > void __weak hw_perf_enable(void) { barrier(); } > > -int __weak > -hw_perf_group_sched_in(struct perf_event *group_leader, > - struct perf_cpu_context *cpuctx, > - struct perf_event_context *ctx) > -{ > - return 0; > -} > - > void __weak perf_event_print_debug(void) { } > > static DEFINE_PER_CPU(int, perf_disable_count); > @@ -642,14 +634,13 @@ group_sched_in(struct perf_event *group_event, > struct perf_event_context *ctx) > { > struct perf_event *event, *partial_group; > + struct pmu *pmu = (struct pmu *)group_event->pmu; > int ret; > > if (group_event->state == PERF_EVENT_STATE_OFF) > return 0; > > - ret = hw_perf_group_sched_in(group_event, cpuctx, ctx); > - if (ret) > - return ret < 0 ? ret : 0; > + pmu->start_txn(pmu); > > if (event_sched_in(group_event, cpuctx, ctx)) > return -EAGAIN; > @@ -664,16 +655,21 @@ group_sched_in(struct perf_event *group_event, > } > } > > - return 0; > + ret = pmu->commit_txn(pmu); > + if (!ret) { > + pmu->stop_txn(pmu); > + return 0; > + } > > group_error: > + pmu->stop_txn(pmu); > + > /* > - * Groups can be scheduled in as one unit only, so undo any > - * partial group before returning: > + * Commit transaction fails, rollback > + * Groups can be scheduled in as one unit only, so undo > + * whole group before returning: > */ > list_for_each_entry(event, &group_event->sibling_list, group_entry) { > - if (event == partial_group) > - break; > event_sched_out(event, cpuctx, ctx); > } > event_sched_out(group_event, cpuctx, ctx); > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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