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SubjectRe: Fix powerTOP regression with 2.6.39-rc5

* Steven Rostedt <rostedt@goodmis.org> wrote:

> > > > PowerTop uses the perf ABI because it's a rather convenient and unified
> > > > method to get a rich selection of events via the same facility, same
> > > > ring-buffer, using a system call ABI, etc.
> > >
> > > It seams that Arjan read the perf kernel code to see how the raw data was
> > > laid out and read it directly.
> >
> > Yes, of course - i also have code that uses the syscall directly, it's
> > easier to code up ad-hoc than to parse some XML-lookalike descriptor from
> > /debug/tracing/events/.
>
> So you admit this is a ad-hoc way of doing things. [...]

There's nothing wrong with being able to code and make use of instrumentation
ad-hoc, using a simple interface.

The *worst* possible thing is to force user-space to use something complex.
So we kept the perf ABI simple.

> [...] Thus a library is a perfect solution. [...]

That's a non sequitor.

> [...] And the event formats are far from XML-look-a-like. You really think
> this:
>
> name: sched_switch
> ID: 57
> format:
> field:unsigned short common_type; offset:0; size:2;
> field:unsigned char common_flags; offset:2; size:1;
> field:unsigned char common_preempt_count; offset:3; size:1;
> field:int common_pid; offset:4; size:4;
> field:int common_lock_depth; offset:8; size:4;
>
> field:char prev_comm[TASK_COMM_LEN]; offset:12; size:16;
> field:pid_t prev_pid; offset:28; size:4;
> field:int prev_prio; offset:32; size:4;
> field:long prev_state; offset:40; size:8;
> field:char next_comm[TASK_COMM_LEN]; offset:48; size:16;
> field:pid_t next_pid; offset:64; size:4;
> field:int next_prio; offset:68; size:4;
>
> Is equivalent to this:
>
> <?xml version="1.0" encoding="UTF-8"?>
> <KernelShark><CaptureSettings><Events><CaptureType>Events</CaptureType><System>sched</System></Events><Plugin>function_graph</Plugin><File>/tmp/trace.dat</File></CaptureSettings></KernelShark>

I did not say that it's equivalent, i said it's XML look-alike.

Steve, we even joked about that, that if we continue like this we'll end up
with an XML parser ... I requested several changes to the description format so
that it becomes more human readable.

Thanks,

Ingo


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