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Date: Sat, 3 Sep 2022 10:14:25 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Tomáš Trnka <trnka@....com>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>
Subject: Re: perf top -p broken for multithreaded processes since 5.19
On 2/09/22 22:17, Arnaldo Carvalho de Melo wrote:
> Em Fri, Sep 02, 2022 at 05:50:22PM +0300, Adrian Hunter escreveu:
>> On 2/09/22 17:46, Tomáš Trnka wrote:
>>> Hello,
>>>
>>> A bug in perf v5.19 and newer completely breaks monitoring multithreaded
>>> processes using "perf top -p". The tool fails to start with "Failed to mmap
>>> with 22 (Invalid argument)". It still seems to work fine on single-threaded
>>> processes. "perf record" is also unaffected.
>>
>> It has been reported here:
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=216441
>
> If I do:
>
> ⬢[acme@...lbox perf-urgent]$ git log -2
> commit dfeb0bc60782471c293938e71b1a1117cfac2cb3 (HEAD -> perf/urgent)
> Author: Arnaldo Carvalho de Melo <acme@...hat.com>
> Date: Fri Sep 2 16:15:39 2022 -0300
>
> Revert "libperf evlist: Check nr_mmaps is correct"
>
> This reverts commit 4ce47d842d4c16c07b135b8a7975b8f0672bcc0e.
>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
>
> commit 78cd283f6b8ab701cb35eafd5af8140560a88f16
> Author: Arnaldo Carvalho de Melo <acme@...hat.com>
> Date: Fri Sep 2 16:13:41 2022 -0300
>
> Revert "libperf evlist: Allow mixing per-thread and per-cpu mmaps"
>
> This reverts commit ae4f8ae16a07896403c90305d4b9be27f657c1fc.
>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ⬢[acme@...lbox perf-urgent]$
>
> It works again, Tomáš can you please try doing this to see if this works
> for you?
>
This is the fix I have so far. I would like to test it some more though.
From: Adrian Hunter <adrian.hunter@...el.com>
Date: Sat, 3 Sep 2022 10:05:08 +0300
Subject: [PATCH] libperf evlist: Fix per-thread mmaps for multi-threaded
targets
Offending commit did not consider the different set-output rules for
per-thread mmaps i.e. in the per-thread case set-output is used for
mmaps of the same thread not the same cpu.
This was not immediately noticed because it only happens with
multi-threaded targets and we do not have a test for that yet.
Fixes: ae4f8ae16a07 ("libperf evlist: Allow mixing per-thread and per-cpu mmaps")
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
tools/lib/perf/evlist.c | 49 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 49 insertions(+)
diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
index e6c98a6e3908e..24280c887520c 100644
--- a/tools/lib/perf/evlist.c
+++ b/tools/lib/perf/evlist.c
@@ -486,6 +486,7 @@ mmap_per_evsel(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
if (ops->idx)
ops->idx(evlist, evsel, mp, idx);
+ pr_debug("idx %d: mmapping fd %d\n", idx, *output);
if (ops->mmap(map, mp, *output, evlist_cpu) < 0)
return -1;
@@ -494,6 +495,7 @@ mmap_per_evsel(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
if (!idx)
perf_evlist__set_mmap_first(evlist, map, overwrite);
} else {
+ pr_debug("idx %d: set output fd %d -> %d\n", idx, fd, *output);
if (ioctl(fd, PERF_EVENT_IOC_SET_OUTPUT, *output) != 0)
return -1;
@@ -519,6 +521,47 @@ mmap_per_evsel(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
return 0;
}
+static int
+mmap_per_thread(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
+ struct perf_mmap_param *mp)
+{
+ int nr_threads = perf_thread_map__nr(evlist->threads);
+ int nr_cpus = perf_cpu_map__nr(evlist->all_cpus);
+ int cpu, thread, idx = 0;
+ int nr_mmaps = 0;
+
+ pr_debug("%s: nr cpu values (may include -1) %d nr threads %d\n", __func__, nr_cpus, nr_threads);
+
+ /* per-thread mmaps */
+ for (thread = 0; thread < nr_threads; thread++, idx++) {
+ int output = -1;
+ int output_overwrite = -1;
+
+ if (mmap_per_evsel(evlist, ops, idx, mp, 0, thread, &output,
+ &output_overwrite, &nr_mmaps))
+ goto out_unmap;
+ }
+
+ /* system-wide mmaps i.e. per-cpu */
+ for (cpu = 1; cpu < nr_cpus; cpu++, idx ++) {
+ int output = -1;
+ int output_overwrite = -1;
+
+ if (mmap_per_evsel(evlist, ops, idx, mp, cpu, 0, &output,
+ &output_overwrite, &nr_mmaps))
+ goto out_unmap;
+ }
+
+ if (nr_mmaps != evlist->nr_mmaps)
+ pr_err("Miscounted nr_mmaps %d vs %d\n", nr_mmaps, evlist->nr_mmaps);
+
+ return 0;
+
+out_unmap:
+ perf_evlist__munmap(evlist);
+ return -1;
+}
+
static int
mmap_per_cpu(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
struct perf_mmap_param *mp)
@@ -528,6 +571,8 @@ mmap_per_cpu(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
int nr_mmaps = 0;
int cpu, thread;
+ pr_debug("%s: nr cpu values %d nr threads %d\n", __func__, nr_cpus, nr_threads);
+
for (cpu = 0; cpu < nr_cpus; cpu++) {
int output = -1;
int output_overwrite = -1;
@@ -569,6 +614,7 @@ int perf_evlist__mmap_ops(struct perf_evlist *evlist,
struct perf_evlist_mmap_ops *ops,
struct perf_mmap_param *mp)
{
+ const struct perf_cpu_map *cpus = evlist->all_cpus;
struct perf_evsel *evsel;
if (!ops || !ops->get || !ops->mmap)
@@ -588,6 +634,9 @@ int perf_evlist__mmap_ops(struct perf_evlist *evlist,
if (evlist->pollfd.entries == NULL && perf_evlist__alloc_pollfd(evlist) < 0)
return -ENOMEM;
+ if (perf_cpu_map__empty(cpus))
+ return mmap_per_thread(evlist, ops, mp);
+
return mmap_per_cpu(evlist, ops, mp);
}
--
2.34.1
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