Messages in this thread Patch in this message | | | From | Kemi Wang <> | Subject | [PATCH v2] buffer: Avoid setting buffer bits that are already set | Date | Tue, 24 Oct 2017 09:16:42 +0800 |
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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> Signed-off-by: Kemi Wang <kemi.wang@intel.com> Tested-by: Kemi Wang <kemi.wang@intel.com> Reviewed-by: Jens Axboe <axboe@kernel.dk> --- include/linux/buffer_head.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index c8dae55..211d8f5 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -80,11 +80,14 @@ 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) \ { \ -- 2.7.4
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