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author | Lukas Czerner <lczerner@redhat.com> | 2013-04-03 22:12:52 -0400 |
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committer | Theodore Ts'o <tytso@mit.edu> | 2013-04-03 22:12:52 -0400 |
commit | 689110098c7df10fab8800d3bf8e727c21f426fb (patch) | |
tree | 4115e575da8b49716e358ebd2459095863ad00e1 /drivers/iommu/Makefile | |
parent | a75ae78f087f933ab3432e98bb4dbbf2196cf6d5 (diff) |
ext4: make ext4_block_in_group() much more efficient
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@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'drivers/iommu/Makefile')
0 files changed, 0 insertions, 0 deletions