diff options
| author |   Kemi Wang <kemi.wang@intel.com> | 2017-10-24 09:16:42 +0800 |
|---|---|---|
| committer |   Jens Axboe <axboe@kernel.dk> | 2018-02-02 07:56:30 -0700 |
| commit | 60f91826ca62bcf85d6d5fc90941337282787671 (patch) | |
| tree | 99c751953bbeb84e3afb40338db1d3df30b90be6 /include/linux/buffer_head.h | |
| parent | blk-mq-sched: Enable merging discard bio into request (diff) | |
| download | linux-dev-60f91826ca62bcf85d6d5fc90941337282787671.tar.xz linux-dev-60f91826ca62bcf85d6d5fc90941337282787671.zip | |
buffer: Avoid setting buffer bits that are already set
It's expensive to set buffer flags that are already set, because that
causes a costly cache line transition.
A common case is setting the "verified" flag during ext4 writes.
This patch checks for the flag being set first.
With the AIM7/creat-clo benchmark testing on a 48G ramdisk based-on ext4
file system, we see 3.3%(15431->15936) improvement of aim7.jobs-per-min on
a 2-sockets broadwell platform.
What the benchmark does is: it forks 3000 processes, and each process do
the following:
a) open a new file
b) close the file
c) delete the file
until loop=100*1000 times.
The original patch is contributed by Andi Kleen.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Tested-by: Kemi Wang <kemi.wang@intel.com>
Signed-off-by: Kemi Wang <kemi.wang@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include/linux/buffer_head.h')
| -rw-r--r-- | include/linux/buffer_head.h | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index 8b1bf8d3d4a2..06797ef10fd9 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -81,11 +81,14 @@ struct buffer_head { /* * macro tricks to expand the set_buffer_foo(), clear_buffer_foo() * and buffer_foo() functions. + * To avoid reset buffer flags that are already set, because that causes + * a costly cache line transition, check the flag first. */ #define BUFFER_FNS(bit, name) \ static __always_inline void set_buffer_##name(struct buffer_head *bh) \ { \ - set_bit(BH_##bit, &(bh)->b_state); \ + if (!test_bit(BH_##bit, &(bh)->b_state)) \ + set_bit(BH_##bit, &(bh)->b_state); \ } \ static __always_inline void clear_buffer_##name(struct buffer_head *bh) \ { \ |