linux-kernel - fresh data was Re: [PATCH] X86-32: Let gcc decide whether to inline memcpy was Re: New x86 warning

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Message-ID: <87skjzoqah.fsf_-_@basil.nowhere.org>
Date:	Thu, 23 Apr 2009 08:08:38 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Jeff Garzik <jeff@...zik.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: fresh data was Re: [PATCH] X86-32: Let gcc decide whether to inline memcpy was Re: New x86 warning

Andi Kleen <andi@...stfloor.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. 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.

-Andi


-- 
ak@...ux.intel.com -- Speaking for myself only.
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