Messages in this thread Patch in this message | | | Date | Fri, 19 Feb 2016 15:37:47 +0100 | From | Peter Zijlstra <> | Subject | [RFC][PATCH 4/7] perf: Fix scaling vs enable_on_exec |
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Oleg reported that enable_on_exec results in weird scale factors.
The recent commit 3e349507d12d ("perf: Fix perf_enable_on_exec() event scheduling") caused this by moving task_ctx_sched_out() from before __perf_event_mask_enable() to after it.
The overlooked concequence of that change is that task_ctx_sched_out() would update the ctx time fields, and now __perf_event_mask_enable() uses stale time.
Fix this by adding an explicit time update.
While looking at this, I also found that we need an ctx->is_active check in perf_install_in_context().
XXX: does this actually fix the reported issue? I'm not sure what the reproduction case is. Also an earlier version made Jiri's machine explode -- something I've not managed to reproduce either.
Fixes: 3e349507d12d ("perf: Fix perf_enable_on_exec() event scheduling") Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/events/core.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-)
--- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2170,12 +2170,12 @@ perf_install_in_context(struct perf_even raw_spin_unlock_irq(&ctx->lock); return; } - update_context_time(ctx); - /* - * Update cgrp time only if current cgrp matches event->cgrp. - * Must be done before calling add_event_to_ctx(). - */ - update_cgrp_time_from_event(event); + + if (ctx->is_active) { + update_context_time(ctx); + update_cgrp_time_from_event(event); + } + add_event_to_ctx(event, ctx); raw_spin_unlock_irq(&ctx->lock); @@ -3122,6 +3122,12 @@ static void perf_event_enable_on_exec(in cpuctx = __get_cpu_context(ctx); perf_ctx_lock(cpuctx, ctx); + + if (ctx->is_active) { + update_context_time(ctx); + update_cgrp_time_from_cpuctx(cpuctx); + } + list_for_each_entry(event, &ctx->event_list, event_entry) enabled |= event_enable_on_exec(event, ctx);
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