From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Clark Williams <williams@redhat.com>,
linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
Adrian Hunter <adrian.hunter@intel.com>,
Jiri Olsa <jolsa@kernel.org>,
Arnaldo Carvalho de Melo <acme@redhat.com>
Subject: [PATCH 29/29] perf session: Add comment for perf_session__register_idle_thread()
Date: Thu, 3 Jan 2019 09:46:09 -0300 [thread overview]
Message-ID: <20190103124609.29672-30-acme@kernel.org> (raw)
In-Reply-To: <20190103124609.29672-1-acme@kernel.org>
From: Adrian Hunter <adrian.hunter@intel.com>
Add a comment to perf_session__register_idle_thread() to bring attention to
a pitfall with the idle task thread structure. The pitfall is that there
should really be a 'struct thread' for the idle task of each cpu, but there
is only one that can have pid == tid == 0.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20181221120620.9659-9-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/session.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 78a067777144..5456c84c7dd1 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1527,6 +1527,13 @@ struct thread *perf_session__findnew(struct perf_session *session, pid_t pid)
return machine__findnew_thread(&session->machines.host, -1, pid);
}
+/*
+ * Threads are identified by pid and tid, and the idle task has pid == tid == 0.
+ * So here a single thread is created for that, but actually there is a separate
+ * idle task per cpu, so there should be one 'struct thread' per cpu, but there
+ * is only 1. That causes problems for some tools, requiring workarounds. For
+ * example get_idle_thread() in builtin-sched.c, or thread_stack__per_cpu().
+ */
int perf_session__register_idle_thread(struct perf_session *session)
{
struct thread *thread;
--
2.19.2
next prev parent reply other threads:[~2019-01-03 12:47 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-03 12:45 [GIT PULL 00/29] perf/core improvements and fixes Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 01/29] perf trace: Check if the raw_syscalls:sys_{enter,exit} are setup before setting tp filter Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 02/29] perf beauty mmap: PROT_WRITE should come before PROT_EXEC Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 03/29] perf build: Don't unconditionally link the libbfd feature test to -liberty and -lz Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 04/29] perf trace: Do not hardcode the size of the tracepoint common_ fields Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 05/29] perf trace: Use correct SECCOMP prefix spelling, "SECOMP_*" -> "SECCOMP_*" Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 06/29] perf python: Do not force closing original perf descriptor in evlist.get_pollfd() Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 07/29] perf script: Fix LBR skid dump problems in brstackinsn Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 08/29] perf trace: Rename thread_thread->paths to thread_trace->files Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 09/29] perf trace: Move the files table resizing to outside set_pathname() Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 10/29] perf trace: Store the major number for a file when storing its pathname Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 11/29] tools headers uapi: Grab a copy of usbdevice_fs.h Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 12/29] perf beauty ioctl: Add generator for USBDEVFS_ ioctl commands Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 13/29] perf trace: Wire up ioctl's USBDEBFS_ cmd table generator Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 14/29] perf trace beauty: Export function to get the files for a thread Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 15/29] perf trace beauty ioctl: Beautify USBDEVFS_ commands Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 16/29] perf c2c: Change the default coalesce setup Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 17/29] perf c2c: Increase the HITM ratio limit for displayed cachelines Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 18/29] tools power x86_energy_perf_policy: Override CFLAGS assignments and add LDFLAGS to build command Arnaldo Carvalho de Melo
2019-01-03 12:45 ` [PATCH 19/29] tools thermal tmon: Allow overriding CFLAGS assignments Arnaldo Carvalho de Melo
2019-01-03 12:46 ` [PATCH 20/29] tools power turbostat: Override CFLAGS assignments and add LDFLAGS to build command Arnaldo Carvalho de Melo
2019-01-03 12:46 ` [PATCH 21/29] tools gpio: Allow overriding CFLAGS Arnaldo Carvalho de Melo
2019-01-03 12:46 ` [PATCH 22/29] perf thread-stack: Simplify some code in thread_stack__process() Arnaldo Carvalho de Melo
2019-01-03 12:46 ` [PATCH 23/29] perf thread-stack: Tidy thread_stack__bottom() usage Arnaldo Carvalho de Melo
2019-01-03 12:46 ` [PATCH 24/29] perf thread-stack: Avoid direct reference to the thread's stack Arnaldo Carvalho de Melo
2019-01-03 12:46 ` [PATCH 25/29] perf thread-stack: Allow for a thread stack array Arnaldo Carvalho de Melo
2019-01-03 12:46 ` [PATCH 26/29] perf thread-stack: Factor out thread_stack__init() Arnaldo Carvalho de Melo
2019-01-03 12:46 ` [PATCH 27/29] perf thread-stack: Allocate an array of thread stacks Arnaldo Carvalho de Melo
2019-01-03 12:46 ` [PATCH 28/29] perf thread-stack: Fix thread stack processing for the idle task Arnaldo Carvalho de Melo
2019-01-03 12:46 ` Arnaldo Carvalho de Melo [this message]
2019-01-03 13:07 ` [GIT PULL 00/29] perf/core improvements and fixes Ingo Molnar
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