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Date: Fri, 3 Nov 2017 10:29:13 +0800 From: kemi <kemi.wang@...el.com> To: Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...com>, Darrick J Wong <darrick.wong@...cle.com>, Eric Biggers <ebiggers@...gle.com>, Andreas Gruenbacher <agruenba@...hat.com>, Jeff Layton <jlayton@...hat.com> Cc: Dave <dave.hansen@...ux.intel.com>, Andi Kleen <andi.kleen@...el.com>, Tim Chen <tim.c.chen@...el.com>, Ying Huang <ying.huang@...el.com>, Aaron Lu <aaron.lu@...el.com>, Linux Kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2] buffer: Avoid setting buffer bits that are already set 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 <ak@...ux.intel.com> > Signed-off-by: Kemi Wang <kemi.wang@...el.com> > Tested-by: Kemi Wang <kemi.wang@...el.com> > Reviewed-by: Jens Axboe <axboe@...nel.dk> > --- 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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