linux-kernel - Re: [RFC PATCH v6 3/5] sched, tracing: reorganize fields of switch event struct

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Date:   Thu, 3 Aug 2023 10:45:33 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ze Gao <zegao2021@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, Ze Gao <zegao@...cent.com>
Subject: Re: [RFC PATCH v6 3/5] sched, tracing: reorganize fields of switch
 event struct

On Thu, 3 Aug 2023 11:51:32 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> > 
> > See the difference?  
> 
> This also doesn't mention you broke the data format for all trace events
> a while back to ensure people are using libtracefs and are thus
> confident this won't break things.


It was the meta data that happened a while ago. As other events change all
the time with this restriction (keeping field names around), I didn't
realize that it was required for this change log. Doesn't hurt adding it.

More details on that:

 commit b000c8065 ("tracing: Remove the extra 4 bytes of padding in events")

This was to get rid of the padding that powertop relied on.

Nit, it's libtraceevent not libtracefs, as libtracefs gets you to the
format files, but it's libtraceveent that parses them.


-- Steve