Messages in this thread | | | Date | Thu, 23 Apr 2009 08:36:25 +0200 | From | Ingo Molnar <> | Subject | Re: fresh data was Re: [PATCH] X86-32: Let gcc decide whether to inline memcpy was Re: New x86 warning |
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* Andi Kleen <andi@firstfloor.org> wrote:
> Andi Kleen <andi@firstfloor.org> writes: > > >> > Quick test here: > >> > >> How about you just compile the kernel with gcc-3.2 and compare the number > >> of calls to memcpy before-and-after instead? That's the real test. > > > > I waited over 10 minutes for the full vmlinux objdumps to finish. sorry lost > > patience. If someone has a fast disassembler we can try it. I'll leave > > them running over night, maybe there are exact numbers tomorrow. > > > > But from a quick check (find -name '*.o' | xargs nm | grep memcpy) there are > > very little files which call it with the patch, so there's some > > evidence that there isn't a dramatic increase. > > I let the objdumps finish over night. [...]
objdump -d never took me more than a minute - let alone a full night. You must be doing something really wrong there. Looking at objdump -d is an essential, unavoidable component of my workflow with x86 architecture patches, you need to find a way to do it efficiently if you want to send patches for this area of the kernel.
> [...] On my setup (defconfig + some additions) there are actually > less calls to out of line memcpy/__memcpy with the patch. I see > only one for my defconfig, while there are ~10 without the patch. > So it makes very little difference. The code size savings must > come from more efficient code generation for the inline case. I > haven't investigated that in detail though. > > So the patch seems like a overall win.
It's a clear loss here with GCC 3.4, and it took me less than 5 minutes to figure that out.
With what precise compiler version did you test (please paste the gcc -v output), and could you send me the precise .config you used, and describe the method you used to determine the number of out-of-line memcpy calls? I'd like to double-check your numbers.
Ingo
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