[lustre-devel] [PATCH 22/37] lustre: lprocfs: use log2.h macros instead of shift loop.
James Simmons
jsimmons at infradead.org
Sun Feb 24 10:09:57 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.
Be aware rounddown_pow_of_two(n) is undefined when "n == 0". We should
handle the "0" case as well. We are aware of this because this case
bit us in the LNet layer.
> 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);
> }
>
>
>
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