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Message-ID: <20130821150916.GA11431@redhat.com>
Date: Wed, 21 Aug 2013 11:09:16 -0400
From: Mike Snitzer <snitzer@...hat.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Stanislaw Gruszka <sgruszka@...hat.com>,
Frederic Weisbecker <fweisbec@...il.com>,
linux-kernel@...r.kernel.org, dm-devel@...hat.com,
Mikulas Patocka <mpatocka@...hat.com>,
"Alasdair G. Kergon" <agk@...hat.com>
Subject: [PATCH] math64: New separate div64_u64_rem helper
Commit f792685006274a850e6cc0ea9ade275ccdfc90bc ("math64: New
div64_u64_rem helper") implemented div64_u64 in terms of div64_u64_rem.
But div64_u64_rem was removed because it slowed down div64_u64 (and
there were no other users of div64_u64_rem).
Device Mapper's I/O statistics support has a need for div64_u64_rem;
reintroduce this helper as a separate method that doesn't slow down
div64_u64, especially on 32-bit systems.
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Cc: Stanislaw Gruszka <sgruszka@...hat.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Mikulas Patocka <mpatocka@...hat.com>
Signed-off-by: Alasdair Kergon <agk@...hat.com>
---
include/linux/math64.h | 13 +++++++++++++
lib/div64.c | 40 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 53 insertions(+), 0 deletions(-)
diff --git a/include/linux/math64.h b/include/linux/math64.h
index 2913b86..69ed5f5 100644
--- a/include/linux/math64.h
+++ b/include/linux/math64.h
@@ -31,6 +31,15 @@ static inline s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
}
/**
+ * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
+ */
+static inline u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
+{
+ *remainder = dividend % divisor;
+ return dividend / divisor;
+}
+
+/**
* div64_u64 - unsigned 64bit divide with 64bit divisor
*/
static inline u64 div64_u64(u64 dividend, u64 divisor)
@@ -63,6 +72,10 @@ static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
extern s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder);
#endif
+#ifndef div64_u64_rem
+extern u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder);
+#endif
+
#ifndef div64_u64
extern u64 div64_u64(u64 dividend, u64 divisor);
#endif
diff --git a/lib/div64.c b/lib/div64.c
index a163b6c..4382ad7 100644
--- a/lib/div64.c
+++ b/lib/div64.c
@@ -79,6 +79,46 @@ EXPORT_SYMBOL(div_s64_rem);
#endif
/**
+ * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
+ * @dividend: 64bit dividend
+ * @divisor: 64bit divisor
+ * @remainder: 64bit remainder
+ *
+ * This implementation is a comparable to algorithm used by div64_u64.
+ * But this operation, which includes math for calculating the remainder,
+ * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
+ * systems.
+ */
+#ifndef div64_u64_rem
+u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
+{
+ u32 high = divisor >> 32;
+ u64 quot;
+
+ if (high == 0) {
+ u32 rem32;
+ quot = div_u64_rem(dividend, divisor, &rem32);
+ *remainder = rem32;
+ } else {
+ int n = 1 + fls(high);
+ quot = div_u64(dividend >> n, divisor >> n);
+
+ if (quot != 0)
+ quot--;
+
+ *remainder = dividend - quot * divisor;
+ if (*remainder >= divisor) {
+ quot++;
+ *remainder -= divisor;
+ }
+ }
+
+ return quot;
+}
+EXPORT_SYMBOL(div64_u64_rem);
+#endif
+
+/**
* div64_u64 - unsigned 64bit divide with 64bit divisor
* @dividend: 64bit dividend
* @divisor: 64bit divisor
--
1.7.4.4
--
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