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SubjectRe: [PATCH 3/3] kmemtrace: Use tracepoints instead of markers.
* Eduard - Gabriel Munteanu (eduard.munteanu@linux360.ro) wrote:
> On Mon, Jan 05, 2009 at 11:05:34AM -0500, Mathieu Desnoyers wrote:
> > Hopefully it does, especially when there are no side-effects. Can you
> > also try with -Os ?
> >
> > Mathieu
>
> Here's the disassembled code when using -Os. It seems it's optimised, as
> with -O2. My GCC's version is 4.3.2 (Gentoo Linux).
>
> If you want to test yourself, the output was generated with 'objdump -d
> -S -a'.
>
> What do you think?
>
> static void print_that(unsigned long num)
> {
> printf("input << 5 == %lu\n", num);
> 40062d: 48 c1 e6 05 shl $0x5,%rsi
> 400631: bf 5e 07 40 00 mov $0x40075e,%edi
> 400636: 31 c0 xor %eax,%eax
> 400638: e8 6b fe ff ff callq 4004a8 <printf@plt>
> sscanf(argv[2], "%lu", &in);
>
> call_do_something(in);
>
> return 0;
> }
> 40063d: 5a pop %rdx
> 40063e: 59 pop %rcx
> 40063f: 31 c0 xor %eax,%eax
> 400641: 5b pop %rbx
> 400642: c3 retq
>
>
> Eduard
>

It looks good. Although I wonder if gcc will still optimize this in more
complicated functions. Just to be 100% sure, I would recommend testing
it in larger functions like schedule() in the kernel tree. But so far it
looks like it does not hurt much to leave a small supplementary operation
in the unlikely() branch.

Mathieu

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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