From: James Clark <james.clark@arm.com>
To: Leo Yan <leo.yan@linaro.org>, Yang Shi <shy828301@gmail.com>
Cc: linux-perf-users@vger.kernel.org,
LAK <linux-arm-kernel@lists.infradead.org>,
coresight@lists.linaro.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
mathieu.poirier@linaro.org, adrian.hunter@intel.com,
Jiri Olsa <jolsa@kernel.org>,
acme@redhat.com, mike.leach@linaro.org,
Will Deacon <will@kernel.org>,
suzuki.poulose@arm.com
Subject: Re: [BUG] perf: No samples found when using kcore + coresight
Date: Thu, 30 Mar 2023 11:36:54 +0100 [thread overview]
Message-ID: <5dc10954-d1ad-e8f8-deff-fd237df48ecb@arm.com> (raw)
In-Reply-To: <6dcf83ad-bfbc-7e59-7c86-bed334bd09e8@arm.com>
On 29/03/2023 17:11, James Clark wrote:
>
>
> On 14/03/2023 00:36, Leo Yan wrote:
>> On Mon, Mar 13, 2023 at 11:15:44AM -0700, Yang Shi wrote:
>>
>> [...]
>>
>>>> Just a quick summary, here we have two issues:
>>>>
>>>> - With command:
>>>> perf record -e cs_etm/@tmc_etf63/k --kcore --per-thread \
>>>> -- taskset --cpu-list 1 uname",
>>>>
>>>> perf doesn't enable "text poke" attribution.
>>>
>>> No, it enables "text poke" and perf fails to decode coresight trace
>>> data too. It doesn't matter whether "--kcore" is after or before "-e
>>> cs/etm/@tmc_etf63/k".
>>
>> Understand now. Thanks for correction, if so we can ignore this one.
>>
>> Leo
>
> To me it looks like it's only --per-thread and --kcore together that
> cause the issue. I can't see if that was mentioned previously in this
> thread.
>
> If it is --per-thread that's causing the issue then I think I have an
> idea why it might be. There are some assumptions and different paths
> taken in decoding in that mode that aren't correct. It causes some other
> issues to do with ordering and timestamps as well and I wanted to fix it
> previously. I wouldn't say that the text-poke change has caused a
> regression, as decoding in this mode was always a bit buggy.
>
> Maybe this is another reason to fix it properly.
Hi Yang,
I found a temporary workaround to the issue. Whenever you use
--per-thread mode, force timeless mode when decoding with --itrace=Z and
it works the same as it did before. For example:
perf report --itrace=Zi1000i
The reason is that the new text poke event was added with timestamps
enabled. The Coresight decoder slightly incorrectly assumed that no
timestamps == per-thread mode so when it sees the new event it goes into
the wrong decode mode.
The assumption was never really correct so I will make a proper fix. But
in the mean time the workaround should be fine.
next prev parent reply other threads:[~2023-03-30 10:37 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAHbLzkrJQTrYBtPkf=jf3OpQ-yBcJe7XkvQstX9j2frz4WF-SQ@mail.gmail.com>
2023-03-07 10:32 ` [BUG] perf: No samples found when using kcore + coresight James Clark
2023-03-07 19:45 ` Yang Shi
2023-03-08 19:56 ` Yang Shi
2023-03-09 11:38 ` Leo Yan
[not found] ` <CAHbLzkpvLHnyL5J5kB_ke3CWVq2=MOEdEQsGex56+Esfgqh1=g@mail.gmail.com>
2023-03-13 12:14 ` Leo Yan
2023-03-13 18:15 ` Yang Shi
2023-03-14 0:36 ` Leo Yan
2023-03-28 0:53 ` Yang Shi
2023-03-28 8:59 ` James Clark
2023-03-28 16:16 ` Yang Shi
2023-03-29 16:08 ` James Clark
2023-03-29 23:25 ` Yang Shi
2023-03-30 8:17 ` James Clark
2023-03-29 16:11 ` James Clark
2023-03-30 10:36 ` James Clark [this message]
2023-03-30 19:54 ` Yang Shi
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