From: Peter Zijlstra <peterz@infradead.org>
To: kan.liang@linux.intel.com
Cc: acme@kernel.org, mingo@redhat.com, linux-kernel@vger.kernel.org,
tglx@linutronix.de, jolsa@kernel.org, eranian@google.com,
alexander.shishkin@linux.intel.com, ak@linux.intel.com,
x86@kernel.org
Subject: [PATCH] x86/math64: Provide a sane mul_u64_u32_div() implementation for x86_64
Date: Wed, 28 Aug 2019 18:11:23 +0200 [thread overview]
Message-ID: <20190828161123.GQ2386@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190828151921.GD17205@worktop.programming.kicks-ass.net>
On Wed, Aug 28, 2019 at 05:19:21PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 26, 2019 at 07:47:35AM -0700, kan.liang@linux.intel.com wrote:
> > + return mul_u64_u32_div(slots, val, 0xff);
>
> But also; x86_64 seems to lack a sane implementation of that function,
> and it currently compiles into utter crap (it can be 2 instructions).
---
Subject: x86/math64: Provide a sane mul_u64_u32_div() implementation for x86_64
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Aug 28 17:39:46 CEST 2019
On x86_64 we can do a u64 * u64 -> u128 widening multiply followed by
a u128 / u64 -> u64 division to implement a sane version of
mul_u64_u32_div().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/div64.h | 13 +++++++++++++
1 file changed, 13 insertions(+)
--- a/arch/x86/include/asm/div64.h
+++ b/arch/x86/include/asm/div64.h
@@ -73,6 +73,19 @@ static inline u64 mul_u32_u32(u32 a, u32
#else
# include <asm-generic/div64.h>
+
+static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 div)
+{
+ u64 q;
+
+ asm ("mulq %2; divq %3" : "=a" (q)
+ : "a" (a), "rm" (mul), "rm" (div)
+ : "rdx");
+
+ return q;
+}
+#define mul_u64_u32_div mul_u64_u32_div
+
#endif /* CONFIG_X86_32 */
#endif /* _ASM_X86_DIV64_H */
next prev parent reply other threads:[~2019-08-28 16:11 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-26 14:47 [RESEND PATCH V3 0/8] TopDown metrics support for Icelake kan.liang
2019-08-26 14:47 ` [RESEND PATCH V3 1/8] perf/x86/intel: Set correct mask for TOPDOWN.SLOTS kan.liang
2019-08-28 7:48 ` Peter Zijlstra
2019-08-26 14:47 ` [RESEND PATCH V3 2/8] perf/x86/intel: Basic support for metrics counters kan.liang
2019-08-28 7:48 ` Peter Zijlstra
2019-08-28 7:52 ` Peter Zijlstra
2019-08-28 13:59 ` Liang, Kan
2019-08-28 8:44 ` Peter Zijlstra
2019-08-28 9:02 ` Peter Zijlstra
2019-08-28 9:37 ` Peter Zijlstra
2019-08-28 13:51 ` Liang, Kan
2019-08-28 8:52 ` Peter Zijlstra
2019-08-26 14:47 ` [RESEND PATCH V3 3/8] perf/x86/intel: Support hardware TopDown metrics kan.liang
2019-08-28 15:02 ` Peter Zijlstra
2019-08-28 19:04 ` Andi Kleen
2019-08-31 9:19 ` Peter Zijlstra
2019-09-09 13:40 ` Liang, Kan
2019-08-28 19:35 ` Liang, Kan
2019-08-28 15:19 ` Peter Zijlstra
2019-08-28 16:11 ` Peter Zijlstra [this message]
2019-08-29 9:30 ` [PATCH] x86/math64: Provide a sane mul_u64_u32_div() implementation for x86_64 Peter Zijlstra
2019-08-28 16:17 ` [RESEND PATCH V3 3/8] perf/x86/intel: Support hardware TopDown metrics Andi Kleen
2019-08-28 16:28 ` Peter Zijlstra
2019-08-29 3:11 ` Andi Kleen
2019-08-29 9:17 ` Peter Zijlstra
2019-08-29 13:31 ` Liang, Kan
2019-08-29 13:52 ` Peter Zijlstra
2019-08-29 16:56 ` Liang, Kan
2019-08-31 9:18 ` Peter Zijlstra
2019-08-30 23:18 ` Stephane Eranian
2019-08-31 0:31 ` Andi Kleen
2019-08-31 9:13 ` Stephane Eranian
2019-08-31 9:29 ` Peter Zijlstra
2019-08-31 17:53 ` Andi Kleen
2019-08-26 14:47 ` [RESEND PATCH V3 4/8] perf/x86/intel: Support per thread RDPMC " kan.liang
2019-08-26 14:47 ` [RESEND PATCH V3 5/8] perf/x86/intel: Export TopDown events for Icelake kan.liang
2019-08-26 14:47 ` [RESEND PATCH V3 6/8] perf/x86/intel: Disable sampling read slots and topdown kan.liang
2019-08-26 14:47 ` [RESEND PATCH V3 7/8] perf, tools, stat: Support new per thread TopDown metrics kan.liang
2019-08-26 14:47 ` [RESEND PATCH V3 8/8] perf, tools: Add documentation for topdown metrics kan.liang
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