[tip:timers/core] math64, timers: Fix 32bit mul_u64_u32_shr() and friends

tip-bot for Peter Zijlstra
2017-01-14T12:52:43Z

Commit-ID: 9e3d6223d2093a8903c8f570a06284453ee59944
Gitweb: http://git.kernel.org/tip/9e3d6223d2093a8903c8f570a06284453ee59944
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Fri, 9 Dec 2016 09:30:11 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 14 Jan 2017 11:31:50 +0100

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: Chris Metcalf <cmetcalf@mellanox.com>
Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>
---
arch/tile/include/asm/Kbuild | 1 -
arch/tile/include/asm/div64.h | 14 ++++++++++++++
arch/x86/include/asm/div64.h | 11 +++++++++++
include/linux/math64.h | 26 ++++++++++++++++++--------
4 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/arch/tile/include/asm/Kbuild b/arch/tile/include/asm/Kbuild
index 2d1f563..20f2ba6 100644
--- a/arch/tile/include/asm/Kbuild
+++ b/arch/tile/include/asm/Kbuild
@@ -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
diff --git a/arch/tile/include/asm/div64.h b/arch/tile/include/asm/div64.h
new file mode 100644
index 0000000..bf61619
--- /dev/null
+++ b/arch/tile/include/asm/div64.h
@@ -0,0 +1,14 @@
+#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 */
diff --git a/arch/x86/include/asm/div64.h b/arch/x86/include/asm/div64.h
index ced283a..af95c47 100644
--- a/arch/x86/include/asm/div64.h
+++ b/arch/x86/include/asm/div64.h
@@ -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 */
diff --git a/include/linux/math64.h b/include/linux/math64.h
index 6e8b5b2..80690c9 100644
--- a/include/linux/math64.h
+++ b/include/linux/math64.h
@@ -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);