[lustre-devel] [PATCH 02/10] lustre: lprocfs: use log2.h macros instead of shift loop.

[James Simmons <jsimmons@infradead.org>]

From: NeilBrown <neilb@suse.com>

These shift loops seem to be trying to avoid doing a
multiplication.
The same effect can be achieved more transparently using
rounddown_pow_of_two().  Even though there is a multiplication
in the C code, the resulting machine code just does a single shift.

As rounddown_pow_of_two() is not defined for 0, and as we cannot be
positively use the blk_size is non-zero, use blk_size ?: 1.

Signed-off-by: NeilBrown <neilb@suse.com>
WC-bug-id: https://jira.whamcloud.com/browse/LU-4423
Reviewed-on: https://review.whamcloud.com/35274
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
---
 fs/lustre/obdclass/lprocfs_status.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/fs/lustre/obdclass/lprocfs_status.c b/fs/lustre/obdclass/lprocfs_status.c
index c5f5807..2b4302e 100644
--- a/fs/lustre/obdclass/lprocfs_status.c
+++ b/fs/lustre/obdclass/lprocfs_status.c
@@ -373,9 +373,7 @@ static ssize_t kbytestotal_show(struct kobject *kobj, struct attribute *attr,
 		u32 blk_size = osfs.os_bsize >> 10;
 		u64 result = osfs.os_blocks;
 
-		while (blk_size >>= 1)
-			result <<= 1;
-
+		result *= rounddown_pow_of_two(blk_size ?: 1);
 		return sprintf(buf, "%llu\n", result);
 	}
 
@@ -396,8 +394,7 @@ static ssize_t kbytesfree_show(struct kobject *kobj, struct attribute *attr,
 		u32 blk_size = osfs.os_bsize >> 10;
 		u64 result = osfs.os_bfree;
 
-		while (blk_size >>= 1)
-			result <<= 1;
+		result *= rounddown_pow_of_two(blk_size ?: 1);
 
 		return sprintf(buf, "%llu\n", result);
 	}
@@ -419,8 +416,7 @@ static ssize_t kbytesavail_show(struct kobject *kobj, struct attribute *attr,
 		u32 blk_size = osfs.os_bsize >> 10;
 		u64 result = osfs.os_bavail;
 
-		while (blk_size >>= 1)
-			result <<= 1;
+		result *= rounddown_pow_of_two(blk_size ?: 1);
 
 		return sprintf(buf, "%llu\n", result);
 	}
-- 
1.8.3.1