On 2012-03-23, at 4:17 PM, Andi Kleen wrote: > We found that the super block cache line containing the extent cache > hit/miss statistics counters is very hot in IO workloads. > > Besides the counter seems racy anyways and can lose updates because > it's not atomic. > > Disabling the counter make a very measurable difference in some IO > micro benchmarks on a 4S system. > > I just disabled it for now because it doesn't seem very useful due > to its racy nature. An alternative would be to turn it into a per > cpu counter, if someone really needs it. > > Simple patch to disable it appended. > > -Andi The patch only disables the statistics counting, but not the sysfs files that will now report bogus statistics. I don't disagree with disabling these stats, but if you are disabling the accounting you should also comment out the functions in fs/ext4/super.c that are printing out these statistics. Cheers, Andreas > --- > > Disable statistics counter in ext4 > > This super bloc cache line is very hot and slows down high IO > workloads. > > Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx> > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > index 74f23c2..7310b0e 100644 > --- a/fs/ext4/extents.c > +++ b/fs/ext4/extents.c > @@ -2049,10 +2049,12 @@ static int ext4_ext_check_cache(struct inode *inode, ext4_lblk_t block, > ret = 1; > } > errout: > +#if 0 > if (!ret) > sbi->extent_cache_misses++; > else > sbi->extent_cache_hits++; > +#endif > trace_ext4_ext_in_cache(inode, block, ret); > spin_unlock(&EXT4_I(inode)->i_block_reservation_lock); > return ret; > > -- > ak@xxxxxxxxxxxxxxx -- Speaking for myself only > -- > 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 -- 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
