linux-kernel - [PATCH 2/2] bitmap: introduce for_each_set

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Message-Id: <20210709034519.2859777-3-yury.norov@gmail.com>
Date:   Thu,  8 Jul 2021 20:45:19 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Tejun Heo <tj@...nel.org>
Subject: [PATCH 2/2] bitmap: introduce for_each_set_bitrange

bitmap_list_string() is very ineffective when printing bitmaps with long
ranges of set bits because it calls find_next_bit for each bit. We can do
better by detecting ranges of set bits.

This patch introduces a macro for_each_set_bitrange and uses it in
bitmap_list_string(). In my environment, before/after is 943008/31008 ns.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 include/linux/find.h |  7 +++++++
 lib/vsprintf.c       | 40 ++++++++++++++++------------------------
 2 files changed, 23 insertions(+), 24 deletions(-)

diff --git a/include/linux/find.h b/include/linux/find.h
index ae9ed52b52b8..1a5ed45dc81b 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -301,6 +301,13 @@ unsigned long find_next_bit_le(const void *addr, unsigned
 	     (bit) < (size);					\
 	     (bit) = find_next_zero_bit((addr), (size), (bit) + 1))
 
+#define for_each_set_bitrange(b, e, addr, size)			\
+	for ((b) = find_next_bit((addr), (size), 0),		\
+	     (e) = find_next_zero_bit((addr), (size), (b) + 1);	\
+	     (b) < (size);					\
+	     (b) = find_next_bit((addr), (size), (e) + 1),	\
+	     (e) = find_next_zero_bit((addr), (size), (b) + 1))
+
 /**
  * for_each_set_clump8 - iterate over bitmap for each 8-bit clump with set bits
  * @start: bit offset to start search and to store the current iteration offset
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 87acf66f0e4c..1ee54dace71e 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1240,38 +1240,30 @@ char *bitmap_list_string(char *buf, char *end, unsigned long *bitmap,
 			 struct printf_spec spec, const char *fmt)
 {
 	int nr_bits = max_t(int, spec.field_width, 0);
-	/* current bit is 'cur', most recently seen range is [rbot, rtop] */
-	int cur, rbot, rtop;
-	bool first = true;
+	char *start = buf;
+	int b, e;
 
 	if (check_pointer(&buf, end, bitmap, spec))
 		return buf;
 
-	rbot = cur = find_first_bit(bitmap, nr_bits);
-	while (cur < nr_bits) {
-		rtop = cur;
-		cur = find_next_bit(bitmap, nr_bits, cur + 1);
-		if (cur < nr_bits && cur <= rtop + 1)
-			continue;
+	for_each_set_bitrange(b, e, bitmap, nr_bits) {
+		buf = number(buf, end, b, default_dec_spec);
+		if (e == b + 1)
+			goto put_comma;
 
-		if (!first) {
-			if (buf < end)
-				*buf = ',';
-			buf++;
-		}
-		first = false;
+		if (buf < end)
+			*buf = '-';
 
-		buf = number(buf, end, rbot, default_dec_spec);
-		if (rbot < rtop) {
-			if (buf < end)
-				*buf = '-';
-			buf++;
+		buf = number(++buf, end, e - 1, default_dec_spec);
+put_comma:
+		if (buf < end)
+			*buf = ',';
+		buf++;
+	}
 
-			buf = number(buf, end, rtop, default_dec_spec);
-		}
+	if (buf > start)
+		buf--;
 
-		rbot = cur;
-	}
 	return buf;
 }
 
-- 
2.30.2