Commit 9e3d6223 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

math64, timers: Fix 32bit mul_u64_u32_shr() and friends 



It turns out that while GCC-4.4 manages to generate 32x32->64 mult
instructions for the 32bit mul_u64_u32_shr() code, any GCC after that
fails horribly.

Fix this by providing an explicit mul_u32_u32() function which can be
architcture provided.

Reported-by: default avatarChris Metcalf <cmetcalf@mellanox.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Chris Metcalf <cmetcalf@mellanox.com> [for tile]
Cc: Christopher S. Hall <christopher.s.hall@intel.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Laurent Vivier <lvivier@redhat.com>
Cc: Liav Rehana <liavr@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Parit Bhargava <prarit@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20161209083011.GD15765@worktop.programming.kicks-ass.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent e96f8f18

arch/tile/include/asm/Kbuild

+0 −1
Original line number Diff line number Diff line
@@ -5,7 +5,6 @@ generic-y += bug.h 
generic-y += bugs.h

generic-y += clkdev.h

generic-y += cputime.h

generic-y += div64.h

generic-y += emergency-restart.h

generic-y += errno.h

generic-y += exec.h

arch/tile/include/asm/div64.h

0 → 100644
+14 −0
Original line number Diff line number Diff line 
#ifndef _ASM_TILE_DIV64_H

#define _ASM_TILE_DIV64_H



#ifdef __tilegx__

static inline u64 mul_u32_u32(u32 a, u32 b)

{

	return __insn_mul_lu_lu(a, b);

}

#define mul_u32_u32 mul_u32_u32

#endif



#include <asm-generic/div64.h>



#endif /* _ASM_TILE_DIV64_H */

arch/x86/include/asm/div64.h

+11 −0
Original line number Diff line number Diff line
@@ -59,6 +59,17 @@ static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder) 
}

#define div_u64_rem	div_u64_rem



static inline u64 mul_u32_u32(u32 a, u32 b)

{

	u32 high, low;



	asm ("mull %[b]" : "=a" (low), "=d" (high)

			 : [a] "a" (a), [b] "rm" (b) );



	return low | ((u64)high) << 32;

}

#define mul_u32_u32 mul_u32_u32



#else

# include <asm-generic/div64.h>

#endif /* CONFIG_X86_32 */

include/linux/math64.h

+18 −8
Original line number Diff line number Diff line
@@ -133,6 +133,16 @@ __iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) 
	return ret;

}



#ifndef mul_u32_u32

/*

 * Many a GCC version messes this up and generates a 64x64 mult :-(

 */

static inline u64 mul_u32_u32(u32 a, u32 b)

{

	return (u64)a * b;

}

#endif



#if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__)



#ifndef mul_u64_u32_shr
@@ -160,9 +170,9 @@ static inline u64 mul_u64_u32_shr(u64 a, u32 mul, unsigned int shift) 
	al = a;

	ah = a >> 32;



	ret = ((u64)al * mul) >> shift;

	ret = mul_u32_u32(al, mul) >> shift;

	if (ah)

		ret += ((u64)ah * mul) << (32 - shift);

		ret += mul_u32_u32(ah, mul) << (32 - shift);



	return ret;

}
@@ -186,10 +196,10 @@ static inline u64 mul_u64_u64_shr(u64 a, u64 b, unsigned int shift) 
	a0.ll = a;

	b0.ll = b;



	rl.ll = (u64)a0.l.low * b0.l.low;

	rm.ll = (u64)a0.l.low * b0.l.high;

	rn.ll = (u64)a0.l.high * b0.l.low;

	rh.ll = (u64)a0.l.high * b0.l.high;

	rl.ll = mul_u32_u32(a0.l.low, b0.l.low);

	rm.ll = mul_u32_u32(a0.l.low, b0.l.high);

	rn.ll = mul_u32_u32(a0.l.high, b0.l.low);

	rh.ll = mul_u32_u32(a0.l.high, b0.l.high);



	/*

	 * Each of these lines computes a 64-bit intermediate result into "c",
@@ -229,8 +239,8 @@ static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 divisor) 
	} u, rl, rh;



	u.ll = a;

	rl.ll = (u64)u.l.low * mul;

	rh.ll = (u64)u.l.high * mul + rl.l.high;

	rl.ll = mul_u32_u32(u.l.low, mul);

	rh.ll = mul_u32_u32(u.l.high, mul) + rl.l.high;



	/* Bits 32-63 of the result will be in rh.l.low. */

	rl.l.high = do_div(rh.ll, divisor);

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