Messages in this thread | | | Date | Mon, 29 Oct 2018 11:35:06 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCHES/RFC] Re: A concern about overflow ring buffer mode |
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Em Mon, Oct 29, 2018 at 10:33:06AM -0400, Liang, Kan escreveu: > On 10/29/2018 9:03 AM, Arnaldo Carvalho de Melo wrote: > > Em Fri, Oct 26, 2018 at 04:11:51PM -0400, Liang, Kan escreveu: > > > On 10/26/2018 3:24 PM, Arnaldo Carvalho de Melo wrote: > > > > Em Fri, Oct 26, 2018 at 03:16:29PM -0400, Liang, Kan escreveu: > > > It is mainly for performance reason to switch to overwrite mode. The impact > > > was very small when I did my test. But now the effect is easily noticeable > > > in other tests. Yes, I agree. We may change it back to non-overwrite mode > > > until the issue is addressed.
> > So, I have these two patches in my perf/core branch, with Fixes tags > > that will make them get to the stable kernels, ok?
> I just realized that the problem in KNL will be back if we switch back to > non-overwrite mode. > The problem is that users have to wait tens of minutes to see perf top > results on the screen in KNL. Before that, there is nothing but a black > screen.
> Sorry I didn't notice it last Friday. Because I thought the ui_warning in > perf_top__mmap_read() can give user a hint. So the user can switch to > overwrite mode manually. > But unfortunately, the ui_warning doesn't work. Because it is called after > perf_top__mmap_read(). The processing time of perf_top__mmap_read() could be > tens of minutes.
So we need a way to notice that we're in a machine like that and warn the user before the wait takes place, ideas on how to do that?
- Arnaldo
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