Messages in this thread | | | Date | Thu, 2 Nov 2017 15:59:11 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH 1/2] perf mmap: Fix perf backward recording |
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On Thu, Nov 02, 2017 at 01:25:08PM +0000, Liang, Kan wrote: > Hi Namhyung, > > > On Wed, Nov 01, 2017 at 04:22:53PM +0000, Liang, Kan wrote: > > > > On 2017/11/1 21:57, Liang, Kan wrote: > > > > >> On 2017/11/1 20:00, Namhyung Kim wrote: > > > > >>> On Wed, Nov 01, 2017 at 06:32:50PM +0800, Wangnan (F) wrote: > > > > > There are only four test cases which set overwrite, > > > > > sw-clock,task-exit, mmap-basic, backward-ring-buffer. > > > > > Only backward-ring-buffer is 'backward overwrite'. > > > > > The rest three are all 'forward overwrite'. We just need to set > > > > > write_backward to convert them to 'backward overwrite'. > > > > > I think it's not hard to clean up. > > > > > > > > If we add a new rule that overwrite ring buffers are always backward > > > > then it is not hard to cleanup. However, the support of forward > > > > overwrite ring buffer has a long history and the code is not written > > > > by me. I'd like to check if there is some reason to keep support this > > configuration? > > > > > > > > > > As my observation, currently, there are no perf tools which support > > > 'forward overwrite'. > > > There are only three test cases (sw-clock, task-exit, mmap-basic) > > > which is set to 'forward overwrite'. I don’t see any reason it cannot > > > be changed to 'backward overwrite' > > > > > > Arnaldo? Jirka? Kim? > > > > > > What do you think? > > > > I think sw-clock, task-exit and mmap-basic test cases can be changed to use > > the forward non-overwrite mode.
agreed, we can change them to forward non-overwrite mode
> > The forward overwrite might be used by externel applications accessing the > > ring buffer directly but not needed for perf tools IMHO. > > The proposal is only for perf tool, not kernel. So external applications can still > use forward overwrite to access the ring buffer. > > > Let's keep the code simpler as much as possible. > > Agree. > Now, there are too many options to access the ring buffer. Not all of them are > supported. > I think we should only keep the crucial options (overwrite/non-overwrite), clearly > define them in the document and cleanup the code.
as you said earlier only 2 modes make sense, so I think perf record should have:
- forward non-overwrite mode by default - backward overwrite mode when '--overwrite' option is set
and make it clear in the docs, maybe in special perf-record man page section
so far I still like the '--overwrite' option more than --flight-recorder' ;-) also it's been out there for some time now
jirka
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