Messages in this thread | | | Date | Mon, 13 Dec 2010 15:51:18 -0200 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header |
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Em Mon, Dec 13, 2010 at 10:36:39AM -0700, David S. Ahern escreveu: > > > On 12/13/10 09:48, Arnaldo Carvalho de Melo wrote: > > Em Mon, Dec 13, 2010 at 04:54:56PM +0100, Frederic Weisbecker escreveu: > >> On Mon, Dec 13, 2010 at 07:39:24AM -0700, David S. Ahern wrote: > >>> Simplest to always add it the header as it does no harm if not used. > >>> To make it conditional means adding an input parameter to > >>> perf_session__new() and then updating all the callers. > > > >>> Is the preference to make it conditional? > > > >> No, I suspect the overhead is plain unnoticeable. And if it becomes > >> any problem one day, we can still make that conditional later. > > > > Right, but it just ocurred to me, can't we encode this in the file stat? > > I would not want to rely on stat output for timestamps. eg., copy that > file off box and not have the timestamp preserved.
Yeah, I should have deleted that part, as I suggested something else after it :-\
> > Also, how do we deal with: > > > > $ perf record --help > > <SNIP> > > -A, --append > > Append to the output file to do incremental profiling. > > <SNIP> > > > > ? > > Is it realistic to expect/allow an append using different perf binaries? > That just seems plain odd. Then, if one invocation used --timehist and > another did not output would be bizarre. Of course an append with a
Well, if you use the existence of a ref time and refuse to append to a file if --timehist is not used, nope.
> reboot between tests would cause problems as well.
Why different perf binaries? Isn't the following scenario valid?
1. perf record --timehist
<stop recording for a while, wait some other time when we know something interesting may happen, some periodic higher load that happens, whatever>
2. perf record -A --timehist
3. use perf report showing the wall clock time and merge it with your app specific log
- Arnaldo
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