Re: btrfs write-bandwidth performance regression of 6.5-rc4/rc3

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

> On Tue, Aug 01, 2023 at 11:51:28PM +0800, Wang Yugui wrote:
> > > Can you try a git-revert of 140fb1f734736a on the latest tree (which
> > > should work cleanly) for an additional data point?
> > 
> > GOOD performance  when btrfs 6.5-rc4 with
> > 	Revert "btrfs: determine synchronous writers from bio or writeback control"
> > 	Revert "btrfs: submit IO synchronously for fast checksum implementations"
> 
> And with only a revert of
> 
> "btrfs: submit IO synchronously for fast checksum implementations"?

GOOD performance when only (Revert "btrfs: submit IO synchronously for fast
checksum implementations") 

> > 
> > GOOD performance  when btrfs 6.5-rc4 with this fix too.
> > diff --git a/fs/btrfs/bio.c b/fs/btrfs/bio.c
> > index 1f3e06ec6924..1b7344e673db 100644
> > --- a/fs/btrfs/bio.c
> > +++ b/fs/btrfs/bio.c
> > @@ -598,7 +598,7 @@ static void run_one_async_free(struct btrfs_work *work)
> >  static bool should_async_write(struct btrfs_bio *bbio)
> >  {
> >         /* Submit synchronously if the checksum implementation is fast. */
> > -       if (test_bit(BTRFS_FS_CSUM_IMPL_FAST, &bbio->fs_info->flags))
> > +       if ((bbio->bio.bi_opf & REQ_META) && test_bit(BTRFS_FS_CSUM_IMPL_FAST, &bbio->fs_info->flags))
> >                 return false;
> 
> This disables synchronous checksum calculation entirely for data I/O.

without this fix, data I/O checksum is always synchronous?
this is a feature change of "btrfs: submit IO synchronously for fast checksum implementations"?


> Also I'm curious if you see any differents for a non-RAID0 (i.e.
> single profile) workload.

'-m single -d single' is about 10% slow that '-m raid1 -d raid0' in this test
case.


Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2023/08/02