Messages in this thread | | | From | Namhyung Kim <> | Date | Mon, 30 Jan 2023 18:13:32 -0800 | Subject | Re: [PATCH 0/4] perf intel-pt: Fix the pipe mode (v1) |
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On Mon, Jan 30, 2023 at 2:56 AM James Clark <james.clark@arm.com> wrote: > > > > On 27/01/2023 23:08, Namhyung Kim wrote: > > Hi James, > > > > On Fri, Jan 27, 2023 at 6:42 AM James Clark <james.clark@arm.com> wrote: > >> > >> > >> > >> On 27/01/2023 07:22, Adrian Hunter wrote: > >>> On 27/01/23 02:19, Namhyung Kim wrote: > >>>> Hello, > >>>> > >>>> I found some problems in Intel-PT and auxtrace in general with pipe. > >>>> In the past it used to work with pipe, but recent code fails. > >>> > >>> Pipe mode is a problem for Intel PT and possibly other auxtrace users. > >> > >> Just some info from my side: For Arm Coresight we ended up deprecating > >> pipe mode, then not supporting it altogether. First was when we added an > >> optional step to peek through all of the data to help with an edge case. > >> Then we added a requirement to receive a HW_ID packet before decoding > >> which necessitated the peek. You can't peek in pipe mode because you > >> need to be able to seek, so it's not supported at all anymore. > >> > >> For Arm SPE I never tested it with piped data. I suppose I could add a > >> test at some point, but I don't really see the usecase. > > > > Yeah, it'd be great if we can have a test for Arm SPE. > > > > Ok thanks I will put it on the list of things to do. > > > Anyway, my work env (Google) requires the pipe mode due to the > > restriction in disk usage. Without the pipe support, it's not possible > > to run `perf record` in production. > > > > Makes sense. Unfortunately at the moment with Coresight, because of the > lack of appropriate timestamps we're waiting for the end of the file > before starting decoding. So you're not really any better off using > piped mode, unless you have a lot more memory than disk space? > > Since this commit [1] and Arm v8.4 we can actually start making use of > the timestamps and do a streaming decode again. So I will also add it to > the list to look into that for Coresight again. Are you using an old > version of Perf or not using Coresight at all? I know Denis at Google is > using Coresight, but only with files rather than pipes.
I'm not aware of usage of Coresight yet in my boundary, but others may be using it.
> > One other thing, have you used the --switch-output mode to perf record > before? I would have said it would give you some of the benefits of > piped mode, but is more likely to work with Coresight. But last time I > checked it's not working either. Not very helpful I know, but something > to keep in mind.
I don't think it'd work because it still occupies the same space. So far, the pipe mode worked well but I think it needs some more improvements.
Anyway, thanks for your suggestion and review!
Thanks, Namhyung
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