[lustre-devel] [PATCH 22/37] lustre: lprocfs: use log2.h macros instead of shift loop.

NeilBrown neilb at suse.com
Mon Feb 18 16:09:06 PST 2019


These shift loops seem to be trying to avoid doing a
multiplication.
We 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.

Signed-off-by: NeilBrown <neilb at suse.com>
---
 .../lustre/lustre/obdclass/lprocfs_status.c        |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
index a179b0d6979e..637aaca96888 100644
--- a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
+++ b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
@@ -341,9 +341,7 @@ 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);
 		return sprintf(buf, "%llu\n", result);
 	}
 
@@ -364,8 +362,7 @@ 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);
 
 		return sprintf(buf, "%llu\n", result);
 	}
@@ -387,8 +384,7 @@ 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);
 
 		return sprintf(buf, "%llu\n", result);
 	}




More information about the lustre-devel mailing list