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Date: Wed, 1 Nov 2017 22:05:20 +0800 From: "Wangnan (F)" <wangnan0@...wei.com> To: "Liang, Kan" <kan.liang@...el.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "acme@...nel.org" <acme@...nel.org>, "jolsa@...hat.com" <jolsa@...hat.com>, "namhyung@...nel.org" <namhyung@...nel.org> Subject: Re: [PATCH 2/2] perf record: Replace 'overwrite' by 'flightrecorder' for better naming On 2017/11/1 21:26, Liang, Kan wrote: >> The meaning of perf record's "overwrite" option and many "overwrite" in >> source code are not clear. In perf's code, the 'overwrite' has 2 meanings: >> 1. Make ringbuffer readonly (perf_evlist__mmap_ex's argument). >> 2. Set evsel's "backward" attribute (in apply_config_terms). >> >> perf record doesn't use meaning 1 at all, but have a overwrite option, its >> real meaning is setting backward. >> > I don't understand here. > 'overwrite' has 2 meanings. perf record only support 1. > It should be a bug, and need to be fixed. Not a bug, but ambiguous. Perf record doesn't need overwrite main channel (we have two channels: evlist->mmap is main channel and evlist->backward_mmap is backward channel), but some testcases require it, and your new patchset may require it. 'perf record --overwrite' doesn't set main channel overwrite. What it does is moving all evsels to backward channel, and we can move some evsels back to the main channel by /no-overwrite/ setting. This behavior is hard to understand. Thank you.
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