Re: [PATCH 3/3] perf test: Add coresight tests to guage quality of data generated

Leo Yan
2022-05-26T08:20:51Z

Hi Carsten,

Sorry for late response.

On Thu, Apr 21, 2022 at 06:38:33PM +0100, Carsten Haitzler wrote:

[...]

> > Very big change... Why squash all patches form previous verion to this
> > single one big patch? Usually the format with small patches is much
> > better for reviewing.
>
> I was asked to re-jig the tree and in doing so I also ended up cutting down
> the size a lot so this just makes more sense together as a "here are the
> tests" as adding infra without any tests makes no sense and the tests
> themelves are self-contained in their own directories and source files and
> "drivign scripts" thus it's essentially patch 1 appended to patch 2 to patch
> 3 etc. and still broken up in the patch file by file.

I am not sure if I understand the meaning, seems to me you could
organize the patch series like:

- Patch for common files (e.g. script lib/coresight.sh or some
Makefile changes);
- Patches for enabling test cases, E.g.:
patch for asm_pure_loop;
patch for thread loop (include unroll loop);
patch for memcpy;
- Patch for documentation.

If this is not comfortable for you, at least we can use three patches:

- Patch for common file (e.g. script lib/coresight.sh);
- Patch for test cases;
- Patch for documentation.

[...]

> > > +If you see these above, then your system is tracing coresight data
> > > +correctly.
> > > +
> > > +To compile perf with coresight support in the perf directory do
> > > +
> > > + make CORESIGHT=1
> >
> > It is inaccurate that if we don't mention openCSD lib.
>
> Do you mean I need to mention that you need the opencsd library installed
> too?

Yes, otherwise, users might directly build perf without opencsd lib,
then finally they cannot use perf with Arm CoreSight.

> > > +This will compile the perf tool with coresight support as well as
> > > +build some small test binaries for perf test. This requires you also
> > > +be compiling for 64bit Arm (ARM64/aarch64). The tools run as part of
> > > +perf coresight tracing are in tests/shell/tools/coresight.
> >
> > For build perf tool, I think above paragraphs are duplicate with the
> > document Documentation/trace/coresight/coresight.rst. Can we simply
> > say:
> >
> > "The details for building perf tool with support Arm Coresight can be
> > found in the "HOWTO.md" file of the openCSD gitHub repository:
> > https://github.com/Linaro/opencsd.
>
> I can. I put this here as I didn't go clone OpencCSD first but used my
> distro OpenCSD packages and thus of course didn't have the documentation in
> front of me. I spent some time wondering why it wasn't building with
> coresight support even though it detected OpenCSD when I compiled... I
> didn't expect to have to go to some separate project git repository and read
> docs there on how to build the perf tool here in the kernel. I wrote this
> because it was an actual problem I hit and it's a lot less frustrating to
> "end users" to give them the information they need in the relevant place
> they need it instead of sending them around to other project trees. Building
> perf with coresight support is handled by the perf tree int he kernel, not
> OpenCSD, thus IMHO that is where the documentation belongs - alongside the
> thing that determines how to build something.

Understand.

> > And "HOWTO.md" file gives the information and examples for how to use
> > perf tool to record and report Coresight trace data. It's the
> > prerequisite for this perf Coresight test."
> >
> > > +You will also want coresight support enabled in your kernel config.
> > > +Ensure it is enabled with:
> > > +
> > > + CONFIG_CORESIGHT=y
> > > +
> > > +There are various other coresight options you probably also want
> > > +enabled like:
> > > +
> > > + CONFIG_CORESIGHT_LINKS_AND_SINKS=y
> > > + CONFIG_CORESIGHT_LINK_AND_SINK_TMC=y
> > > + CONFIG_CORESIGHT_CATU=y
> > > + CONFIG_CORESIGHT_SINK_TPIU=y
> > > + CONFIG_CORESIGHT_SINK_ETBV10=y
> > > + CONFIG_CORESIGHT_SOURCE_ETM4X=y
> > > + CONFIG_CORESIGHT_STM=y
> > > + CONFIG_CORESIGHT_CPU_DEBUG=y
> > > + CONFIG_CORESIGHT_CTI=y
> > > + CONFIG_CORESIGHT_CTI_INTEGRATION_REGS=y
> > > +
> > > +Please refer to the kernel configuration help for more information.
> >
> > I prefer to remove these kernel configuration since they are not
> > inconsistent on different platforms (e.g. ETBV10, ETM4X, etc), and
> > some configurations might not necessary (e.g. CPU_DEBUG).
>
> Certainly there should be some documentation on which kernel configs you
> might want to turn on then? Imagine someone new comes along and doesn't have
> any idea what to possible enable at all and manages to build perf with
> coresight support (as above) then finds it doesn't work because they didn't
> enable enough config in the kernel? Sure - could probably trim these down a
> bit but the point here is to alert the user to there being a range of
> coresight config options that you need to turn on that you likely will find
> are not turned on. They certainly are not turned on on distro kernels and a
> lot of the time when you have a platform that already boots/works you start
> with your distro kernel config file because you want everything enabled so
> it actually boots. I've learned the hard way to do this as you manage to
> forget to turn on some MMC driver or some other feature and your boot hangs
> or doesn't find rootfs etc.

So far, we will have two documents in Linux kernel:

- Documentation/trace/coresight/coresight.rst;
- tools/perf/Documentation/arm-coresight.txt.

We need to avoid overlap between these two files. I think we could use
the file Documentation/trace/coresight/coresight.rst to focus on
CoreSight driver module relates stuffs and
tools/perf/Documentation/arm-coresight.txt is more about the perf
usages.

But, the file Documentation/trace/coresight/coresight.rst doesn't give
any info for kernel configs, I think which would be a better place to
give information for building kernel modules.

> What would you recommend then as a "turn these on and coresight will almost
> certainly work for you on your given hardware " then?

This would be fine. Alternatively, we could add a section in the file
Documentation/trace/coresight/coresight.rst to describe how to build
CoreSight modules.

How you think for this? I also would like to get suggestions from
CoreSight maintainers Suzuki/Mathieu/Mike.

[...]

> > Please update based on the latest test case names, at my side, I can
> > see the testing case like:
> >
> > Coresight / ASM Pure Loop
> > Coresight / Memcpy 16k 10 Threads
> > Coresight / Thread Loop 10 Threads - Check TID
> > Coresight / Thread Loop 2 Threads - Check TID
> > Coresight / Unroll Loop Thread 10
>
> Oh sorry - yeah. I wrote the docs based on the earlier tests. Will fix.

Thanks.

> > > +
> > > +These perf record tests will not run if the tool binaries do not exist
> > > +in tests/shell/tools/coresight/*/ and will be skipped. If you do not
> > > +have coresight support in hardware then either do not build perf with
> > > +coresight support or remove these binaries in order to not have these
> > > +tests fail and have them skip instead.
> > > +
> > > +These tests will log historical results in the current working
> > > +directory (e.g. tools/perf) and will be named stats-*.csv like:
> > > +
> > > + stats-asm_pure_loop-out.csv
> > > + stats-bubble_sort-random.csv
> > > + ...
> > > +
> > > +These statistic files log some aspects of the AUX data sections in
> > > +the perf data output counting some numbers of certain encodings (a
> > > +good way to know that it's working in a very simple way). One problem
> > > +with coresight is that given a large enough amount of data needing to
> > > +be logged, some of it can be lost due to the processor not waking up
> > > +in time to read out all the data from buffers etc.. You will notice
> > > +that the amount of data collected can vary a lot per run of perf test.
> > > +If you wish to see how this changes over time, simply run perf test
> > > +multiple times and all these csv files will have more and more data
> > > +appended to it that you can later examine, graph and otherwise use to
> > > +figure out if things have become worse or better.
> >
> > I am confused by this narrative. Does it try to remind that the final
> > testing result (pass or fail) is not stable? Or should we run for
> > multiple times so have more chance to capture issues?
>
> That is correct. I thought I was clear that it's lossy. That is actually the
> case. I have tests here that actually fail because there is no data
> collected from some threads at all (missing CID blocks for some of the
> threads that run in the test). The point is to have tests that may be
> failing now but in future will improve. I lowered the minimum bar to pass
> for most tests to have "at least just a little data" but most tests show
> highly variable amount of captured data. the csv files are there to
> over-time give you a good idea of the stability of the captured data.

Okay, this would be fine for me. Though I am a bit worry that later if
users report a failure, then how we can tell them this is a bug or it's
just tracing quality issue?

[...]

> > > diff --git a/tools/perf/tests/shell/coresight/asm_pure_loop/.gitignore b/tools/perf/tests/shell/coresight/asm_pure_loop/.gitignore
> > > new file mode 100644
> > > index 000000000000..468673ac32e8
> > > --- /dev/null
> > > +++ b/tools/perf/tests/shell/coresight/asm_pure_loop/.gitignore
> > > @@ -0,0 +1 @@
> > > +asm_pure_loop
> >
> > Do we really need there '.gitignore' files under the folder
> > 'tools/perf/tests/shell/coresight/'.
>
> Where would you rather have them to ignore the generated binary tools?

It's interesting that I wanted to find a case to object you, so I tried
to check the folder linux/samples/bpf, but it does use .gitignore file
to ignore built binaries :)

Adding .gitignore is in practice and this would be fine for me.

> > > diff --git a/tools/perf/tests/shell/coresight/asm_pure_loop/Makefile b/tools/perf/tests/shell/coresight/asm_pure_loop/Makefile
> > > new file mode 100644
> > > index 000000000000..10c5a60cb71c
> > > --- /dev/null
> > > +++ b/tools/perf/tests/shell/coresight/asm_pure_loop/Makefile
> > > @@ -0,0 +1,30 @@
> > > +# SPDX-License-Identifier: GPL-2.0
> > > +# Carsten Haitzler <carsten.haitzler@arm.com>, 2021
> > > +
> > > +include ../Makefile.miniconfig
> > > +
> > > +BIN=asm_pure_loop
> > > +LIB=
> >
> > Remove the unused variable 'LIB='.
>
> I have this because I wanted to have a simple template to be able to re-use
> for more tests over time. It's so much easier to maintain and extend if
> every makefile and tool follow a similar pattern and you can almost copy &
> paste between them as they don't have "exceptions". You really want me to
> remove this?

It's fine to keep it. Could you add a comment for this?

To be honest, I am not experienced for bash shell script, so I have no
idea why write like this way. If you think this is very common usage
in shell, then you could keep it and don't need to add comment.

[...]

> > There have four sub folders under tools/perf/tests/shell/coresight:
> >
> > asm_pure_loop
> > memcpy_thread
> > thread_loop
> > unroll_loop_thread
> >
> > And every folder has its own Makefile and every Makefile is quite
> > close to each other. I am just wandering if it's possible to
> > remove the 4 Makefiles in these four sub folders, and simply use
> > tools/perf/tests/shell/coresight/Makefile as the central place to
> > build these assistant programs.
>
> I did this so it's easier to etxent over time. having a single parent
> makefile that over time accumulates little ugly "if's" and exceptions makes
> longer-term maintenance and extending harder. I did it this way to make this
> easy - make a copy of a dir - add that dir to a parent makefile then modify
> the makefile as needed (but only as needed).

Okay, let's keep the saperate makefiles.

> > > diff --git a/tools/perf/tests/shell/coresight/asm_pure_loop/asm_pure_loop.S b/tools/perf/tests/shell/coresight/asm_pure_loop/asm_pure_loop.S
> > > new file mode 100644
> > > index 000000000000..75cf084a927d
> > > --- /dev/null
> > > +++ b/tools/perf/tests/shell/coresight/asm_pure_loop/asm_pure_loop.S
> > > @@ -0,0 +1,28 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > +/* Tamas Zsoldos <tamas.zsoldos@arm.com>, 2021 */
> > > +
> > > +.globl _start
> > > +_start:
> > > + mov x0, 0x0000ffff
> > > + mov x1, xzr
> > > +loop:
> > > + nop
> > > + nop
> > > + cbnz x1, noskip
> > > + nop
> > > + nop
> > > + adrp x2, skip
> > > + add x2, x2, :lo12:skip
> > > + br x2
> > > + nop
> > > + nop
> > > +noskip:
> > > + nop
> > > + nop
> > > +skip:
> > > + sub x0, x0, 1
> > > + cbnz x0, loop
> > > +
> > > + mov x0, #0
> > > + mov x8, #93 // __NR_exit syscall
> > > + svc #0
> >
> > I tested the case "ASM Pure Loop" on my Juno board, and it complaints:
> >
> > root@debian:/mnt/export/arm-linux-kernel/tools/perf# ./perf test -v 76
> > 76: Coresight / ASM Pure Loop :
> > --- start ---
> > test child forked, pid 9063
> > failed to mmap with 12 (Cannot allocate memory)
> > test child finished with -1
> > ---- end ----
> > Coresight / ASM Pure Loop: FAILED!
> >
> > Since I only setup the 1GB memory for the Linux kernel, it fails to
> > allocate AUX ring buffer with the size 256MB. So I manully change
> > the buffer size to 8MB in tools/perf/tests/shell/lib/coresight.sh:
> >
> > PERFRECMEM="-m ,8M"
> >
> > So finally I can see the test case is passed:
>
> This is artificial isn't it? limiting to 1GB. You certainly have far more
> memory than that available. My testse were on a system with 4GB and I had no
> issues.

Please see below comment.

> > root@debian:/mnt/export/arm-linux-kernel/tools/perf# ./perf test -v 76
> > 76: Coresight / ASM Pure Loop :
> > --- start ---
> > test child forked, pid 9481
> > -m ,8M -e cs_etm//u
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.681 MB ./perf-asm_pure_loop-out.data ]
> > test child finished with 0
> > ---- end ----
> > Coresight / ASM Pure Loop: Ok
> >
> > Do you think we really need to use 256MiB as the AUX buffer size?
> > IIRC, it means we allocate 256MiB per CPU for this case, on the other
> > hand, you could see the final perf data file size is small (0.681
> > MiB).
> >
> > Seems to me, it's not necessary to allocate so big buffer for
> > the test, and I tried to run below 4 cases with 8MiB, all of them can
> > pass the testing :)
>
> I didn't think anyone with a system with coresight support that would be
> running perf record locally would only have 1GB of ram... I knew junos had
> 8GB and my dragonboard has 4GB ... so I know I was on the smaller side. I
> thought a larger buffer == safer results (less chance of needing to write
> out the buffer during capture). Admittdly I used 256Mb when my tests ran for
> much longer and collected more data. I can try drop to 8 or 16gb and see.

Yes, my Juno board has 8GB but I also have DB410c with 1GB with quad
coes [1]. I am still concern for 256MB buffer size, it's not friendly for
embedded system, and even not good for server. For example, if we run
this testing on Arm server with 96 cores (like Hisilicon D06 board),
then we need the buffer size is:

256MiB * 96 = 16GiB

I agree usually 16GiB is not a problem for server, but seems to me
it doesn't make much sense to consume huge memory resource for the
testing.

In other words, if set 8MiB (or 16MiB, 32MiB) buffer size and doesn't
see testing result regression, I think this would be good to decrease
the buffer size.

[1] https://www.96boards.org/product/dragonboard410c/

[...]

> > > diff --git a/tools/perf/tests/shell/coresight_asm_pure_loop.sh b/tools/perf/tests/shell/coresight_asm_pure_loop.sh
> > > new file mode 100755
> > > index 000000000000..3f0dbefcad50
> > > --- /dev/null
> > > +++ b/tools/perf/tests/shell/coresight_asm_pure_loop.sh
> > > @@ -0,0 +1,18 @@
> > > +#!/bin/sh -e
> > > +# Coresight / ASM Pure Loop
> > > +
> > > +# SPDX-License-Identifier: GPL-2.0
> > > +# Carsten Haitzler <carsten.haitzler@arm.com>, 2021
> > > +
> > > +TEST="asm_pure_loop"
> > > +. $(dirname $0)/lib/coresight.sh
> > > +ARGS=""
> > > +DATV="out"
> > > +DATA="$DATD/perf-$TEST-$DATV.data"
> > > +
> > > +perf record $PERFRECOPT -o "$DATA" "$BIN" $ARGS
> > > +
> > > +perf_dump_aux_verify "$DATA" 10 10 10
> > > +
> > > +err=$?
> > > +exit $err
> >
> > Can we organize the shell scripts by moving them into the folder
> > tools/perf/tests/shell/coresight?
>
> We can - but it comes with a fair few more changes.
>
> > coresight_asm_pure_loop.sh
> > coresight_memcpy_thread_16k_10.sh
> > coresight_thread_loop_check_tid_10.sh
> > coresight_thread_loop_check_tid_2.sh
> > coresight_unroll_loop_thread_10.sh
> >
> > And we even can consider to move script test_arm_coresight.sh into
> > the folder tools/perf/tests/shell/coresight and change its
> > name as 'coresight_smoke_test.sh'.
>
> Indeed these other tests I left alone for now and had not thought about how
> to marry these together yet - leaving this for another day and another patch
> set rather than this patch set itself. That was my thoguht. I was trying to
> make an "Easier to extend by just dropping a test into a dir" setup here to
> make maintenance and expansion easier over time (and thus encourage testing
> by having a simple repeatable test infra to duplicate). I ended up with a
> dir per test tool you need to build and a driver script in the tests/shell
> dir. I think this is certainly worth considering but perhaps as a separate
> set of work to marry these?

Okay, it would be fine to use separate set for moving the script
test_arm_coresight.sh, which is a simple case.

> I piggybacked on the existing shell test infra but added a fair few more
> scripts. To do what you suggest I'd need to modify the core shell test code
> to walk subdirs recursively then looking for child scripts. The problem is
> how does perf test's shell handling know about the coresight subdir vs the
> lib subdir?

Yeah, now I understand your point. How about file layout like below?

tools/perf/tests/shell/coresight_test_hub.sh
tools/perf/tests/shell/coresight/coresight_asm_pure_loop.sh
tools/perf/tests/shell/coresight/coresight_memcpy_thread_16k_10.sh
tools/perf/tests/shell/coresight/coresight_thread_loop_check_tid_10.sh
tools/perf/tests/shell/coresight/coresight_thread_loop_check_tid_2.sh
tools/perf/tests/shell/coresight/coresight_unroll_loop_thread_10.sh

So we use tools/perf/tests/shell/coresight_test_hub.sh as an interface
to hook with Perf test infrastructure, and then hub.sh file calls
testing scripts under the sub folder. Seems to me, this is also
friendly for later's extension.

> Both contain *.sh shell scripts - the difference is the ones in
> lib are not executable. Is this sufficiently different? I could also open
> them to check the have #!/bin/... as the first line. Hardcoding just a
> single coresight subdir just feels wrong and hacky to me, thus the generic
> recursion solution I suggest here.

Agreed. I also don't prefer this way.

> I can definitely see how extending to subdirs would make supporting testing
> cleaner and divide things into their own domains (dirs).

Thanks a lot for the work! The test cases are good for me (but I would
say Mike is the best person for reviewing testing trace data quaility),
I just want to make sure it's not hard for later maintenance.

Leo