linux-kernel - find_new_bit bloat from x86 tree...

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Message-Id: <20080426.220726.13692428.davem@davemloft.net>
Date:	Sat, 26 Apr 2008 22:07:26 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	linux-kernel@...r.kernel.org
CC:	mingo@...e.hu, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, viro@...IV.linux.org.uk
Subject: find_new_bit bloat from x86 tree...


Ingo, what the heck is this?

commit 64970b68d2b3ed32b964b0b30b1b98518fde388e
Author: Alexander van Heukelum <heukelum@...lshack.com>
Date:   Tue Mar 11 16:17:19 2008 +0100

    x86, generic: optimize find_next_(zero_)bit for small constant-size bitmaps

Thanks for bloating up the inline expansion of this thing on every
architecture that doesn't do __ffs() in a simple sequence of a few
instructions like x86 does.

Now every call that matches your tests gets this turd inline:

static inline unsigned long __ffs(unsigned long word)
{
	int num = 0;

#if BITS_PER_LONG == 64
	if ((word & 0xffffffff) == 0) {
		num += 32;
		word >>= 32;
	}
#endif
	if ((word & 0xffff) == 0) {
		num += 16;
		word >>= 16;
	}
	if ((word & 0xff) == 0) {
		num += 8;
		word >>= 8;
	}
	if ((word & 0xf) == 0) {
		num += 4;
		word >>= 4;
	}
	if ((word & 0x3) == 0) {
		num += 2;
		word >>= 2;
	}
	if ((word & 0x1) == 0)
		num += 1;
	return num;
}

as well as all of that address formation, bit shifting, and masking.

Please revert or make this conditional on something architectures can
opt-in for.

The version actually applied was posted only on linux-kernel, instead
of also CC:'ing linux-arch as previous versions had been.  Nobody
commented on this version other than you Ingo.
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