Messages in this thread | | | Date | Fri, 19 Apr 2019 09:04:40 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] compiler.h, tracing: Remove CONFIG_PROFILE_ALL_BRANCHES |
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On Fri, 19 Apr 2019 12:08:37 +0200 Ingo Molnar <mingo@kernel.org> wrote:
> > Can't you just have those same engineers look at perf data? This seems > > like a very expensive and convoluted way of getting something.
I haven't tried the perf data. How well does it work with running over a 2 weeks to a month period? That's what I do yearly. Here's the results of my last run:
http://rostedt.homelinux.com/branches/gandalf-branches-2019/brach_all-2019-02-05
http://rostedt.homelinux.com/branches/mammoth-branches-2019/branch_all-2019-01-02 http://rostedt.homelinux.com/branches/mammoth-branches-2019/branch_all-2019-01-03 http://rostedt.homelinux.com/branches/mammoth-branches-2019/branch_all-2019-01-17 http://rostedt.homelinux.com/branches/mammoth-branches-2019/branch_all-2019-02-05
I have a cron job that runs nightly that copies the current state, and if the machine reboots, it starts a new file (which is why there's multiple files for mammoth - it rebooted).
> > So since no-one offered objections to using perf branch profiling instead > (which method allows so much more than CONFIG_PROFILE_ALL_BRANCHES: such
I've never used it, so I have no idea if it is suitable or not.
> as profiling glibc and other user-space, or allowing to branch-profile > the kernel is an uninstrumented form not distorted by > CONFIG_PROFILE_ALL_BRANCHES code generation artifacts), lemme propose the > attached patch to remove if-tracing. > > If the CONFIG_PROFILE_ALL_BRANCHES=y feature is required for anyone it > can still be reverted privately or maintained out of tree - no need to > burden the mainline kernel with this.
But is it a real burden? It's been in the kernel for over 10 years with very little issue. Only when we do something drastic does it show up, and it's usually a quick fix to get it working again.
I believe Josh even told me that it found a bug in the objtool code, so it does still have benefit staying in the kernel even without people using it for profiling.
Note, I'm in the middle of writing a LWN article about learning the kernel from branch profiling and it would be a shame if it disappears before I finish it.
-- Steve
> > I've build tested this and it Looks Perfect Here™.
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