Messages in this thread | | | Subject | Re: [PATCH 03/10] perf tool: new iterfaces to read event from ring buffer | From | "Wangnan (F)" <> | Date | Wed, 11 Oct 2017 03:22:30 +0800 |
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On 2017/10/11 3:17, Arnaldo Carvalho de Melo wrote: > Em Wed, Oct 11, 2017 at 03:10:37AM +0800, Wangnan (F) escreveu: >> >> On 2017/10/11 3:00, Arnaldo Carvalho de Melo wrote: >>> Em Tue, Oct 10, 2017 at 03:36:28PM -0300, Arnaldo Carvalho de Melo escreveu: >>>> Em Tue, Oct 10, 2017 at 03:34:55PM -0300, Arnaldo Carvalho de Melo escreveu: >>>>> Em Tue, Oct 10, 2017 at 06:28:18PM +0000, Liang, Kan escreveu: >>>>>>> Em Tue, Oct 10, 2017 at 10:20:16AM -0700, kan.liang@intel.com escreveu: >>>>>>>> From: Kan Liang <kan.liang@intel.com> >>>>>>>> >>>>>>>> The perf_evlist__mmap_read only support forward mode. It needs a >>>>>>>> common function to support both forward and backward mode. >>>>>>>> The perf_evlist__mmap_read_backward is buggy. >>>>>>> So, what is the bug? You state that it is buggy, but don't spell out the bug, >>>>>>> please do so. >>>>>>> >>>>>> union perf_event *perf_evlist__mmap_read_backward(struct perf_evlist *evlist, int idx) >>>>>> { >>>>>> struct perf_mmap *md = &evlist->mmap[idx]; <--- it should be backward_mmap >>>>>> >>>>>>> If it fixes an existing bug, then it should go separate from this patchkit, right? >>>>>> There is no one use perf_evlist__mmap_read_backward. So it doesn't trigger any issue. >>>>> There is no one at the end of your patchkit? Or no user _right now_? If >>>>> there is a user now, lemme see... yeah, no user right now, so _that_ is >>>>> yet another bug, i.e. it should be used, no? If this is just a left >>>>> over, then we should just throw it away, now, its a cleanup. >>>> Wang, can you take a look at these two issues? >>> So it looks leftover that should've been removed by the following cset, right Wang? >>> commit a0c6f451f90204847ce5f91c3268d83a76bde1b6 >>> Author: Wang Nan <wangnan0@huawei.com> >>> Date: Thu Jul 14 08:34:41 2016 +0000 >>> perf evlist: Drop evlist->backward >>> Now there's no real user of evlist->backward. Drop it. We are going to >>> use evlist->backward_mmap as a container for backward ring buffer. > >> Yes, it should be removed, but then there will be no corresponding >> function to perf_evlist__mmap_read(), which read an record from forward >> ring buffer. > >> I think Kan wants to become the first user of this function because >> he is trying to make 'perf top' utilizing backward ring buffer. It needs >> perf_evlist__mmap_read_backward(), and he triggers the bug use his >> unpublished patch set. > >> I think we can remove it now, let Kan fix and add it back in his 'perf top' >> patch set. > Well, if there will be a user, perhaps we should fix it, as it seems > interesting to have now for, as you said, a counterpart for the forward > ring buffer, and one that we have plans for using soon, right?
Right if I understand Kan's patch 00/10 correctly. He said:
... But perf top need to switch to overwrite backward mode for good performance. ...
Thank you.
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