This is a note to let you know that I've just added the patch titled
perf/core: Fix time tracking bug with multiplexing
to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-core-fix-time-tracking-bug-with-multiplexing.patch
and it can be found in the queue-4.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 8fdc65391c6ad16461526a685f03262b3b01bfde Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Tue, 29 Mar 2016 09:26:44 +0200
Subject: perf/core: Fix time tracking bug with multiplexing
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
commit 8fdc65391c6ad16461526a685f03262b3b01bfde upstream.
Stephane reported that commit:
3cbaa5906967 ("perf: Fix ctx time tracking by introducing EVENT_TIME")
introduced a regression wrt. time tracking, as easily observed by:
> This patch introduce a bug in the time tracking of events when
> multiplexing is used.
>
> The issue is easily reproducible with the following perf run:
>
> $ perf stat -a -C 0 -e branches,branches,branches,branches,branches,branches -I 1000
> 1.000730239 652,394 branches (66.41%)
> 1.000730239 597,809 branches (66.41%)
> 1.000730239 593,870 branches (66.63%)
> 1.000730239 651,440 branches (67.03%)
> 1.000730239 656,725 branches (66.96%)
> 1.000730239 <not counted> branches
>
> One branches event is shown as not having run. Yet, with
> multiplexing, all events should run especially with a 1s (-I 1000)
> interval. The delta for time_running comes out to 0. Yet, the event
> has run because the kernel is actually multiplexing the events. The
> problem is that the time tracking is the kernel and especially in
> ctx_sched_out() is wrong now.
>
> The problem is that in case that the kernel enters ctx_sched_out() with the
> following state:
> ctx->is_active=0x7 event_type=0x1
> Call Trace:
> [<ffffffff813ddd41>] dump_stack+0x63/0x82
> [<ffffffff81182bdc>] ctx_sched_out+0x2bc/0x2d0
> [<ffffffff81183896>] perf_mux_hrtimer_handler+0xf6/0x2c0
> [<ffffffff811837a0>] ? __perf_install_in_context+0x130/0x130
> [<ffffffff810f5818>] __hrtimer_run_queues+0xf8/0x2f0
> [<ffffffff810f6097>] hrtimer_interrupt+0xb7/0x1d0
> [<ffffffff810509a8>] local_apic_timer_interrupt+0x38/0x60
> [<ffffffff8175ca9d>] smp_apic_timer_interrupt+0x3d/0x50
> [<ffffffff8175ac7c>] apic_timer_interrupt+0x8c/0xa0
>
> In that case, the test:
> if (is_active & EVENT_TIME)
>
> will be false and the time will not be updated. Time must always be updated on
> sched out.
Fix this by always updating time if EVENT_TIME was set, as opposed to
only updating time when EVENT_TIME changed.
Reported-by: Stephane Eranian <eranian@xxxxxxxxxx>
Tested-by: Stephane Eranian <eranian@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: kan.liang@xxxxxxxxx
Cc: namhyung@xxxxxxxxxx
Fixes: 3cbaa5906967 ("perf: Fix ctx time tracking by introducing EVENT_TIME")
Link: http://lkml.kernel.org/r/20160329072644.GB3408@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/events/core.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2402,14 +2402,24 @@ static void ctx_sched_out(struct perf_ev
cpuctx->task_ctx = NULL;
}
- is_active ^= ctx->is_active; /* changed bits */
-
+ /*
+ * Always update time if it was set; not only when it changes.
+ * Otherwise we can 'forget' to update time for any but the last
+ * context we sched out. For example:
+ *
+ * ctx_sched_out(.event_type = EVENT_FLEXIBLE)
+ * ctx_sched_out(.event_type = EVENT_PINNED)
+ *
+ * would only update time for the pinned events.
+ */
if (is_active & EVENT_TIME) {
/* update (and stop) ctx time */
update_context_time(ctx);
update_cgrp_time_from_cpuctx(cpuctx);
}
+ is_active ^= ctx->is_active; /* changed bits */
+
if (!ctx->nr_active || !(is_active & EVENT_ALL))
return;
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-4.5/x86-edac-sb_edac.c-repair-damage-introduced-when-fixing-channel-address.patch
queue-4.5/efi-expose-non-blocking-set_variable-wrapper-to-efivars.patch
queue-4.5/sched-cgroup-fix-cleanup-cgroup-teardown-init.patch
queue-4.5/asm-generic-futex-re-enable-preemption-in-futex_atomic_cmpxchg_inatomic.patch
queue-4.5/x86-mm-kmmio-fix-mmiotrace-for-hugepages.patch
queue-4.5/perf-hists-browser-fix-dump-to-show-correct-callchain-style.patch
queue-4.5/perf-hists-browser-only-offer-symbol-scripting-when-a-symbol-is-under-the-cursor.patch
queue-4.5/perf-tools-fix-perf-script-python-database-export-crash.patch
queue-4.5/perf-core-fix-time-tracking-bug-with-multiplexing.patch
queue-4.5/x86-mce-avoid-using-object-after-free-in-genpool.patch
queue-4.5/x86-edac-sb_edac.c-take-account-of-channel-hashing-when-needed.patch
queue-4.5/futex-handle-unlock_pi-race-gracefully.patch
queue-4.5/perf-stat-document-detailed-option.patch
queue-4.5/perf-core-don-t-leak-event-in-the-syscall-error-path.patch
queue-4.5/locking-mcs-fix-mcs_spin_lock-ordering.patch
queue-4.5/futex-acknowledge-a-new-waiter-in-counter-before-plist.patch
queue-4.5/x86-mm-xen-suppress-hugetlbfs-in-pv-guests.patch
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