On 2017年10月24日 09:16, Kemi Wang wrote:
> 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 <[email protected]>
> Signed-off-by: Kemi Wang <[email protected]>
> Tested-by: Kemi Wang <[email protected]>
> Reviewed-by: Jens Axboe <[email protected]>
> ---
Seems that this patch is still not merged. Anything wrong with that? thanks
> 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) \
> { \
>
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