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>

diff --git a/arch/tile/include/asm/Kbuild b/arch/tile/include/asm/Kbuild
index 2d1f5638974cded6c3311945e8741d047bf2d4e9..20f2ba6d79be0374217ddd0282ba07b26b4cd3c3 100644 (file)
--- 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 (file)
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 ced283ac79dfff3ca6c580da509136845ed1ce5b..af95c47d5c9ef6ccb2617226535f63761e8039ef 100644 (file)
--- 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 6e8b5b270ffeada870b3cdcd638530f2479b84ee..80690c96c734d4fea4cd8970fe6a93b89eb34379 100644 (file)
--- 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);