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From: Peter Zijlstra <peterz@infradead.org>
To: kan.liang@linux.intel.com
Cc: acme@redhat.com, mingo@kernel.org, linux-kernel@vger.kernel.org,
	jolsa@kernel.org, eranian@google.com,
	alexander.shishkin@linux.intel.com, ak@linux.intel.com
Subject: Re: [PATCH V6 11/14] perf/x86/intel: Disable sample-read the slots and metrics events
Date: Tue, 21 Jul 2020 15:10:11 +0200	[thread overview]
Message-ID: <20200721131011.GY10769@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200717140554.22863-12-kan.liang@linux.intel.com>

On Fri, Jul 17, 2020 at 07:05:51AM -0700, kan.liang@linux.intel.com wrote:
> From: Kan Liang <kan.liang@linux.intel.com>
> 
> Users fail to sample-read the slots and metrics events, e.g.,
> perf record -e '{slots, topdown-retiring}:S'.
> 
> When reading the metrics event, the fixed counter 3 (slots) has to be
> reset, which impacts the sampling of the slots event.
> 
> Add a specific validate_group() support to reject the case and error out
> for Ice Lake.
> 
> An alternative fix may unconditionally disable slots sampling, but it's
> not a decent fix. Users may want to only sample the slot events
> without the topdown metrics events.
> 
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>

I'm confused by this; it doesn't make sense.

Should not patch 7 have something like the below instead?

Also, I think there is a bug when we create a group like this and then
kill the leader, in that case the core code will 'promote' the sibling
metric events to their own individual events, see perf_group_detach().

We need additional code to move those events into unrecoverable ERROR
state. A new group_caps flag could indicate this promotion isn't
allowed.

--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3441,8 +3441,22 @@ static int intel_pmu_hw_config(struct pe
 	 * A flag PERF_X86_EVENT_TOPDOWN is applied for the case.
 	 */
 	if (x86_pmu.intel_cap.perf_metrics && is_topdown_event(event)) {
-		if (is_metric_event(event) && is_sampling_event(event))
-			return -EINVAL;
+
+		if (is_metric_event(event)) {
+			struct perf_event *leader = event->group_leader;
+
+			if (is_sampling_event(event))
+				return -EINVAL;
+
+			if (leader == event)
+				return -EINVAL;
+
+			if (!is_slots_event(leader))
+				return -EINVAL;
+
+			if (is_sampling_event(leader))
+				return -EINVAL;
+		}
 
 		if (!is_sampling_event(event)) {
 			if (event->attr.config1 != 0)

  reply	other threads:[~2020-07-21 13:10 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 14:05 [PATCH V6 00/14] TopDown metrics support for Icelake kan.liang
2020-07-17 14:05 ` [PATCH V6 01/14] perf/x86: Use event_base_rdpmc for the RDPMC userspace support kan.liang
2020-07-17 14:05 ` [PATCH V6 02/14] perf/x86/intel: Name the global status bit in NMI handler kan.liang
2020-07-17 14:05 ` [PATCH V6 03/14] perf/x86/intel: Introduce the fourth fixed counter kan.liang
2020-07-20 16:20   ` Peter Zijlstra
2020-07-20 18:22     ` Liang, Kan
2020-07-17 14:05 ` [PATCH V6 04/14] perf/x86/intel: Move BTS index to 47 kan.liang
2020-07-17 14:05 ` [PATCH V6 05/14] perf/x86/intel: Fix the name of perf METRICS kan.liang
2020-07-17 14:05 ` [PATCH V6 06/14] perf/x86/intel: Use switch in intel_pmu_disable/enable_event kan.liang
2020-07-20 16:22   ` Peter Zijlstra
2020-07-20 19:02     ` Liang, Kan
2020-07-17 14:05 ` [PATCH V6 07/14] perf/x86/intel: Generic support for hardware TopDown metrics kan.liang
2020-07-20 17:41   ` Peter Zijlstra
2020-07-20 18:11     ` Liang, Kan
2020-07-21  9:43   ` Peter Zijlstra
2020-07-21 14:05     ` Liang, Kan
2020-07-21 14:25       ` peterz
2020-07-17 14:05 ` [PATCH V6 08/14] perf/x86: Add a macro for RDPMC offset of fixed counters kan.liang
2020-07-17 14:05 ` [PATCH V6 09/14] perf/x86/intel: Support TopDown metrics on Ice Lake kan.liang
2020-07-21 12:40   ` Peter Zijlstra
2020-07-21 14:23     ` Liang, Kan
2020-07-21 14:31       ` peterz
2020-07-21 15:50         ` Liang, Kan
2020-07-21 17:38     ` Andi Kleen
2020-07-21 19:20       ` Peter Zijlstra
2020-07-17 14:05 ` [PATCH V6 10/14] perf/x86/intel: Support per-thread RDPMC TopDown metrics kan.liang
2020-07-17 14:05 ` [PATCH V6 11/14] perf/x86/intel: Disable sample-read the slots and metrics events kan.liang
2020-07-21 13:10   ` Peter Zijlstra [this message]
2020-07-21 16:07     ` Liang, Kan
2020-07-21 19:18       ` Peter Zijlstra
2020-07-22 19:26     ` Liang, Kan
2020-07-17 14:05 ` [PATCH V6 12/14] perf, tools, stat: Support new per thread TopDown metrics kan.liang
2020-07-17 14:05 ` [PATCH V6 13/14] perf, tools, stat: Check Topdown Metric group kan.liang
2020-07-17 14:05 ` [PATCH V6 14/14] perf, tools: Add documentation for topdown metrics kan.liang

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