RE: [PATCH] perf cs-etm: Fix missing decoder for per-process trace

[Besar Wicaksono]

Hi James,

Please see my comment inline.

> -----Original Message-----
> From: James Clark <james.clark@xxxxxxx>
> Sent: Tuesday, September 26, 2023 5:57 AM
> To: Besar Wicaksono <bwicaksono@xxxxxxxxxx>; mike.leach@xxxxxxxxxx;
> suzuki.poulose@xxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> coresight@xxxxxxxxxxxxxxxx; linux-tegra@xxxxxxxxxxxxxxx; Thierry Reding
> <treding@xxxxxxxxxx>; Jonathan Hunter <jonathanh@xxxxxxxxxx>; Vikram
> Sethi <vsethi@xxxxxxxxxx>; Richard Wiley <rwiley@xxxxxxxxxx>; Yifei Wan
> <ywan@xxxxxxxxxx>
> Subject: Re: [PATCH] perf cs-etm: Fix missing decoder for per-process trace
> 
> External email: Use caution opening links or attachments
> 
> 
> On 19/09/2023 23:45, Besar Wicaksono wrote:
> > The decoder creation for raw trace uses metadata from the first CPU.
> > On per-process/per-thread traces, the first CPU is CPU0. If CPU0 trace
> > is not enabled, its metadata will be marked unused and the decoder is
> > not created. Perf report dump skips the decoding part because the
> > decoder is missing.
> >
> 
> Hi Besar,
> 
> It's not just per-process trace, the bug is also in per-cpu mode but it
> means that the metadata from CPU 0 is used for every decoder which is
> wrong. Although your change also fixes this issue.
> 

Got it, I will update the commit message on V2.

> > To fix this, use metadata of the CPU associated with sample object.
> >
> > Signed-off-by: Besar Wicaksono <bwicaksono@xxxxxxxxxx>
> > ---
> >  tools/perf/util/cs-etm.c | 130 +++++++++++++++++++++++----------------
> >  1 file changed, 77 insertions(+), 53 deletions(-)
> >
> 
> [...]
> 
> > +     if (!formatted) {
> > +             /*
> > +              * There is only one decoder when unformatted. Use metadata of
> > +              * sample AUX cpu.
> > +              */
> > +             t_param = t_params;
> > +             metadata = get_cpu_data(etm, sample_cpu);
> > +             if (!metadata) {
> > +                     pr_err("CS_ETM: invalid sample CPU: %d\n", sample_cpu);
> >                       return -EINVAL;
> >               }
> 
> Apart from Mike's comments, this looks ok. Thanks for fixing this it has
> been on our list for a while.
> 
> One issue with calling get_cpu_data() with the sample CPU ID is that it
> won't work with old files that don't have the CPU sample flag set. Mike
> added the sample flag fairly recently, and I don't think that was a
> breaking change for old files at that time. It should be easy to avoid
> that by still returning the metadata from CPU 0 when CPU = -1 (Which
> isn't correct but is 99% likely to work).
> 

Thanks for the feedback, I will add this check and debug message to indicate
the missing cpu id.

> I checked the Coresight tests and they're all passing, at least on a
> system without ETE. If you could make sure they're all passing for you
> as well that would be great:
> 
>   sudo ./perf test coresight
> 
> I think they currently only work from an in source build, if you get
> stuck there.
> 

The test looks ok on my system. Here is what I got:

74: CoreSight / ASM Pure Loop                                       : Ok
 75: CoreSight / Memcpy 16k 10 Threads                               : Ok
 76: CoreSight / Thread Loop 10 Threads - Check TID                  : Ok
 77: CoreSight / Thread Loop 2 Threads - Check TID                   : Ok
 78: CoreSight / Unroll Loop Thread 10                               : Ok
103: Check Arm CoreSight trace data recording and synthesized samples: Ok

Thanks,
Besar