Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <CAHbLzkrJQTrYBtPkf=jf3OpQ-yBcJe7XkvQstX9j2frz4WF-SQ@mail.gmail.com>
 <8ca2b07e-674e-afb6-ff12-87504f51f252@arm.com> <CAHbLzkpf4RUZugKdn-uXC5m3RpAQH5aDmRXdsxPZi0Cbf-yiyw@mail.gmail.com>
 <CAHbLzkq_7aXcys1cpgGFsfMDDDKMsT3e7zdNW=0jAkw7kBtJ0Q@mail.gmail.com>
 <20230309113851.GF19253@leoy-yangtze.lan> <CAHbLzkpvLHnyL5J5kB_ke3CWVq2=MOEdEQsGex56+Esfgqh1=g@mail.gmail.com>
 <20230313121420.GB2426758@leoy-yangtze.lan> <CAHbLzkpZjrd401DEKnnCNMdra0f6kGRe1Nh_rTovNTmyD8aBpg@mail.gmail.com>
 <20230314003610.GD2426758@leoy-yangtze.lan> <6dcf83ad-bfbc-7e59-7c86-bed334bd09e8@arm.com>
 <5dc10954-d1ad-e8f8-deff-fd237df48ecb@arm.com>
In-Reply-To: <5dc10954-d1ad-e8f8-deff-fd237df48ecb@arm.com>
From:   Yang Shi <shy828301@gmail.com>
Date:   Thu, 30 Mar 2023 12:54:25 -0700
Message-ID: <CAHbLzkqrEQoK_NDfHVO8tdBT1Lycpia5dcAVuiJBeDdx+jtzaQ@mail.gmail.com>
Subject: Re: [BUG] perf: No samples found when using kcore + coresight
To:     James Clark <james.clark@arm.com>
Cc:     Leo Yan <leo.yan@linaro.org>, 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
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, Mar 30, 2023 at 3:36=E2=80=AFAM James Clark <james.clark@arm.com> w=
rote:
>
>
>
> 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 othe=
r
> > issues to do with ordering and timestamps as well and I wanted to fix i=
t
> > 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=3DZ an=
d
> it works the same as it did before. For example:
>
>   perf report --itrace=3DZi1000i
>
> The reason is that the new text poke event was added with timestamps
> enabled. The Coresight decoder slightly incorrectly assumed that no
> timestamps =3D=3D per-thread mode so when it sees the new event it goes i=
nto
> 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.

Hi James,

Thanks for figuring out the workaround. I tested both (using "-C"
instead of "--per-thread" for record or using "--itrace=3DZ" for report)
works. I think the workaround is fine before we have a proper fix.

>