Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1439532

Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace

Show all headers | View raw

* Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> On Fri, Jul 08, 2016 at 12:08:19PM +0200, Ingo Molnar wrote:
> > 
> > * Byungchul Park <byungchul.park@lge.com> wrote:
> > 
> > > On Mon, Jul 04, 2016 at 07:27:54PM +0900, Byungchul Park wrote:
> > > > I suggested this patch on https://lkml.org/lkml/2016/6/20/22. However,
> > > > I want to proceed saperately since it's somewhat independent from each
> > > > other. Frankly speaking, I want this patchset to be accepted at first so
> > > > that the crossfeature can use this optimized save_stack_trace_norm()
> > > > which makes crossrelease work smoothly.
> > > 
> > > What do you think about this way to improve it?
> > 
> > I like both of your improvements, the speed up is impressive:
> > 
> >   [    2.327597] save_stack_trace() takes 87114 ns
> >   ...
> >   [    2.781694] save_stack_trace() takes 20044 ns
> >   ...
> >   [    3.103264] save_stack_trace takes 3821 (sched_lock)
> > 
> > Could you please also measure call graph recording (perf record -g), how much 
> > faster does it get with your patches and what are our remaining performance hot 
> > spots?
> > 
> > Could you please merge your patches to the latest -tip tree, because this commit I 
> > merged earlier today:
> > 
> >   81c2949f7fdc x86/dumpstack: Add show_stack_regs() and use it
> > 
> > conflicts with your patches. (I'll push this commit out later today.)
> > 
> > Also, could you please rename the _norm names to _fast or so, to signal that this 
> > is a faster but less reliable method to get a stack dump? Nobody knows what 
> > '_norm' means, but '_fast' is pretty self-explanatory.
> 
> Hm, but is print_context_stack_bp() variant really less reliable?  From
> what I can tell, its only differences vs print_context_stack() are:
> 
> - It doesn't scan the stack for "guesses" (which are 'unreliable' and
>   are ignored by the ops->address() callback anyway).
> 
> - It stops if ops->address() returns an error (which in this case means
>   the array is full anyway).
> 
> - It stops if the address isn't a kernel text address.  I think this
>   shouldn't normally be possible unless there's some generated code like
>   bpf on the stack.  Maybe it could be slightly improved for this case.
> 
> So instead of adding a new save_stack_trace_fast() variant, why don't we
> just modify the existing save_stack_trace() to use
> print_context_stack_bp()?

Ok, agreed!

Thanks,

	Ingo

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Byungchul Park <byungchul.park@lge.com> - 2016-07-04 12:30 +0200
  [PATCH 2/2] x86/dumpstack: Add save_stack_trace_norm() Byungchul Park <byungchul.park@lge.com> - 2016-07-04 12:30 +0200
  Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Byungchul Park <byungchul.park@lge.com> - 2016-07-07 12:20 +0200
    Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Ingo Molnar <mingo@kernel.org> - 2016-07-08 12:10 +0200
      Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-08 16:30 +0200
        Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Ingo Molnar <mingo@kernel.org> - 2016-07-08 16:50 +0200
        Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Frederic Weisbecker <fweisbec@gmail.com> - 2016-07-08 17:20 +0200
          Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-08 17:30 +0200
            Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Byungchul Park <byungchul.park@lge.com> - 2016-07-18 05:20 +0200
              Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-18 15:10 +0200
                Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Byungchul Park <byungchul.park@lge.com> - 2016-07-19 02:20 +0200
          Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Byungchul Park <byungchul.park@lge.com> - 2016-07-18 04:50 +0200
      Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Frederic Weisbecker <fweisbec@gmail.com> - 2016-07-08 17:10 +0200
      Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Byungchul Park <byungchul.park@lge.com> - 2016-07-18 04:40 +0200
  Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-08 16:10 +0200
  Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Frederic Weisbecker <fweisbec@gmail.com> - 2016-07-08 16:50 +0200
    Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace Byungchul Park <byungchul.park@lge.com> - 2016-07-18 05:30 +0200

csiph-web