Messages in this thread | | | Date | Fri, 5 Sep 2008 07:57:03 -0700 | From | Arjan van de Ven <> | Subject | Re: frame unwinder patches |
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On Fri, 5 Sep 2008 16:48:52 +0200 Bernd Schubert <bs@q-leap.de> wrote:
> On Friday 05 September 2008 16:13:37 Arjan van de Ven wrote: > > On Fri, 5 Sep 2008 15:52:47 +0200 > > > > Bernd Schubert <bs@q-leap.de> wrote: > > > > (and if you really care it's 1 line of code to turn it off) > > > > > > It is not only this, I think the dwarf2 stack unwinder patches > > > provide by far better traces than the in-kernel unwinder. At least > > > ever since I applied these patches to our kernels, I was able to > > > read the stack dumps... > > > > they really wouldn't be different than the ones you get if you > > remove the "?" lines. > > Well may be, but then there is still the performace degrading, so I > don't want to have it enabled on our production kernels. I admit I > never measured what is the difference between of > CONFIG_FRAME_POINTER=y and =n, but the fact the help text says there > is a difference already makes me want to disable it (especially, > since we have to provide benchmarks before we can sell a system).
to be honest, on 64 bit the overhead is quite small (the extra instructions it adds are optimized for by the modern cpus that you use in the systems you're selling); on 32 bit the overhead is.. well a little bigger but not THAT much. yes it loses a register for the compiler to use, but no it's not a general purpose register, and with the register renaming that today's cpus do, I'd be surprised if you could see anything significant.
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