On Wed, 2007-07-18 at 20:18 -0700, Andrew Morton wrote: > On Fri, 13 Jul 2007 18:36:54 -0700 Badari Pulavarty <pbadari@xxxxxxxxxx> wrote: > > > More statfs() improvements for ext2. ext2 already maintains > > percpu counters for free blocks and inodes. Derive free > > block count and inode count by summing up percpu counters, > > instead of counting up all the groups in the filesystem > > each time. > > > > hm, another speedup patch with no measurements which demonstrate its > benefit. In my setups (4 & 8-way), I didn't measure any significant performance improvements (in any reasonable workload). I see some decent improvements on cooked-up (1 million stats) tests :( > > > > > Signed-off-by: Badari Pulavarty <pbadari@xxxxxxxxxx> > > Acked-by: Andreas Dilger <adilger@xxxxxxxxxxxxx> > > > > fs/ext2/super.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > Index: linux-2.6.22/fs/ext2/super.c > > =================================================================== > > --- linux-2.6.22.orig/fs/ext2/super.c 2007-07-13 20:06:38.000000000 -0700 > > +++ linux-2.6.22/fs/ext2/super.c 2007-07-13 20:06:51.000000000 -0700 > > @@ -1136,12 +1136,12 @@ static int ext2_statfs (struct dentry * > > buf->f_type = EXT2_SUPER_MAGIC; > > buf->f_bsize = sb->s_blocksize; > > buf->f_blocks = le32_to_cpu(es->s_blocks_count) - overhead; > > - buf->f_bfree = ext2_count_free_blocks(sb); > > + buf->f_bfree = percpu_counter_sum(&sbi->s_freeblocks_counter); > > buf->f_bavail = buf->f_bfree - le32_to_cpu(es->s_r_blocks_count); > > if (buf->f_bfree < le32_to_cpu(es->s_r_blocks_count)) > > buf->f_bavail = 0; > > buf->f_files = le32_to_cpu(es->s_inodes_count); > > - buf->f_ffree = ext2_count_free_inodes(sb); > > + buf->f_ffree = percpu_counter_sum(&sbi->s_freeinodes_counter); > > buf->f_namelen = EXT2_NAME_LEN; > > fsid = le64_to_cpup((void *)es->s_uuid) ^ > > le64_to_cpup((void *)es->s_uuid + sizeof(u64)); > > > > Well there's a tradeoff here. At large CPU counts, percpu_counter_sum() > becomes quite expensive - it takes a global lock and then goes off fishing > in every CPU's percpu_alloced memory. > > So there is some value of (num_online_cpus / sb->s_groups_count) at which > this change becomes a loss. Where does that value lie? Yes. I debated long time whether I should submit this or not - due to very reason. Old code wasn't holding any locks. I don't have any high count CPU machine (>8way) with me. I will request for time on one. > > Bear in mind that the global lock in percpu_counter_sum() will tilt the > scales quite a bit. Noticed that too. I added WARN_ON() to see if percpu sum doesn't match computed sum. I saw few stacks in a 24 hour run of fsx runs. Thanks, Badari - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
