Hi,
Is this a linux distribution or an android running on a linux kernel for android?
I'm running a linux distribution, Debian Buster
What is "sinkid=0xa6509eae" ?
It's the sinkid corresponding to tmc_etr0. When casting the perf command using @tmc_etr0 unfortunately I'm displayed the following error:

$ perf record --per-thread -e cs_etm/@tmc_etr/u  -- ls
>> failed to set sink "" on event cs_etm/@tmc_etr/u with 21 (Is a directory)

so I found myself forced to manually specify the identifier.
I think this problem has been solved in the latest kernel versions but I still have to double check.

My CoreSight subsystem is the following:

$ ls /sys/bus/coresight/devices/
> etm0  etm1  etm2  etm3  etm4  etm5  etm6  etm7  funnel0  funnel1  funnel2  funnel3  funnel4  replicator0  stm0  tmc_etf0  tmc_etr0

$ grep . /sys/devices/cs_etm/sinks/*
/sys/devices/cs_etm/sinks/tmc_etf0:0x97979549
/sys/devices/cs_etm/sinks/tmc_etr0:0xa6509eae

To allow the "--mmap-pages" to work with big buffer, the sink needs
to directly output trace data to DDR, you also need to take care
what's the buffer mode you are using (flat, sg, CATU).
Thanks for the suggestion! Is there a way for me to enforce this?
Is it possible to check out how much data I'm losing/overwriting?
Do you know what is the best buffer mode for avoiding losing data?
How can I switch between a buffer mode and another one?
Is `--per-thread` the best way to trace a single-threaded workload?

Thanks everybody for the interest on this!
Andrea
From: Mathieu Poirier <mathieu.poirier@linaro.org>
Sent: 04 March 2020 02:43
To: leo.yan@linaro.org <leo.yan@linaro.org>
Cc: Andrea Brunato <Andrea.Brunato@arm.com>; coresight@lists.linaro.org <coresight@lists.linaro.org>
Subject: Re: perf record cs_etm: data lost
 
On Tue, 3 Mar 2020 at 18:54, Leo Yan <leo.yan@linaro.org> wrote:
>
> Hi Andrea,
>
> On Tue, Mar 03, 2020 at 11:23:29AM -0700, Mathieu Poirier wrote:
> > Hi Andrea,
> >
> > On Tue, 3 Mar 2020 at 09:34, Andrea Brunato <Andrea.Brunato@arm.com> wrote:
> > >
> > > Good afternoon,
> > >
> > > When using perf to record a simple benchmark I see the following warning:
> > >
> > > $ perf record --per-thread -e cs_etm/sinkid=0xa6509eae/u  ~/afdo/coremark/coremark/coremark.exe  0x3415 0x3415 0x66 0 7 1 2000  > run2.log
> >
> > What is "sinkid=0xa6509eae" ?
>
> Sink might be ETF/ETR/ETB, I think this is why Mathieu asked the meaning
> for 'sinkid', which we don't which sink you are using.
>
> > > [ perf record: Woken up 6 times to write data ]
> > > Warning:
> > > AUX data lost 6 times out of 6!
> > >
> > > [ perf record: Captured and wrote 0.378 MB perf.data ]
> > >
> > > This is on DB845c (https://www.96boards.org/product/rb3-platform/), kernel 5.5.0-rc7.
> > >
> > > It looks like perf is losing data and the reported perf.data file is very tiny, given that the application runs for several seconds.
> > > Does anybody have any idea about what it may be causing this?
>
> Just give some info based on my understanding.
>
> For the log "AUX data lost 6 times out of 6!", since you are using
> per-thread mode, so every time when the task switching out, the trace
> data in the sink will be read out and save into aux buffer.  But
> usually the sink's buffer is not big (maximum to MBs), so it's easily
> to overwrite the hardware's cycle buffer and the previous trace data
> will be lost.  For this reason, it reports "AUX data lost".
>
> > > I've tried adding --mmap-pages=32K,64K to the command for increasing the buffer size, but it's not actually solving the problem
>
> If it's the overflow in the hardware buffer in SRAM, "--mmap-pages"
> option doesn't work, since it only enlarges aux buffer page size but
> cannot change the SRAM size in CoreSight.
>
> To allow the "--mmap-pages" to work with big buffer, the sink needs
> to directly output trace data to DDR, you also need to take care
> what's the buffer mode you are using (flat, sg, CATU).

Everything Leo said above is accurate.

>
> Thanks,
> Leo
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