From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Date: Wed, 27 Feb 2019 11:51:26 +1100 Subject: [lustre-devel] [PATCH 22/37] lustre: lprocfs: use log2.h macros instead of shift loop. In-Reply-To: References: <155053473693.24125.6976971762921761309.stgit@noble.brown> <155053494599.24125.1795878344125234751.stgit@noble.brown> Message-ID: <87k1hmt5o1.fsf@notabene.neil.brown.name> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lustre-devel@lists.lustre.org On Tue, Feb 26 2019, James Simmons wrote: >> 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". Hmm... can os_bsize ever be less than 1024? I guess we still need to be careful of the possibility. The current code treats anything less than 1024 as though it were 1024, so I could achieve the same thing with result *= rounddown_pow_of_two(blk_size ?: 1); Is that too obscure? Thanks, NeilBrown > >> Signed-off-by: NeilBrown >> --- >> .../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); >> } >> >> >> -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 832 bytes Desc: not available URL: