On Wed, Mar 27, 2013 at 04:35:40PM +0100, Lukas Czerner wrote: > Currently in when getting the block group number for a particular block > in ext4_block_in_group() we're using ext4_get_group_no_and_offset() > which uses do_div() to get the block group and the remainer which is > offset within the group. > > We don't need all of that in ext4_block_in_group() as we only need to > figure out the group number. > > This commit changes ext4_block_in_group() to calculate group number > directly. This shows as a big improvement with regards to cpu > utilization. Measuring fallocate -l 15T on fresh file system with perf > showed that 23% of cpu time was spend in the > ext4_get_group_no_and_offset(). With this change it completely > disappears from the list only bumping the occurrence of > ext4_init_block_bitmap() which is the biggest user of > ext4_block_in_group() by 4%. As the result of this change on my system > the fallocate call was approx. 10% faster. > > However since there is '-g' option in mkfs which allow us setting > different groups size (mostly for developers) I've introduced new per > file system flag whether we have a standard block group size or not. The > flag is used to determine whether we can use the bit shift optimization > or not. > > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx> Thanks, applied. - Ted -- 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
