Hi Ian,
On Tue, Dec 22, 2020 at 3:47 PM Ian Kent <raven@xxxxxxxxxx> wrote:
>
> Here is what I currently have for the patch series we were discussing
> recently.
>
> I'm interested to see how this goes with the problem you are seeing.
>
> The last patch in the series (the attributes update patch) has seen
> no more than compile testing, I hope I haven't messed up on that.
OK, I just ignored the last patch (kernfs: add a spinlock to kernfs
iattrs for inode updates)
because I can not boot the kernel after applying it.
Applying the first five patches, my benchmark shows no improvement this time,
one open+read+close cycle spends 500us. :(
perf suggests that down_write in kernfs_iop_permission drags the most
performance
(full report see attachment) which makes sense to me, since down_write
has no difference
here compared to the mutex, they all allow only one thread running
simultaneously.
sigh... It's really hard to fix.
|
|--51.81%--inode_permission
| |
| --51.36%--kernfs_iop_permission
| |
| |--50.41%--down_write
| | |
| | --50.32%--rwsem_down_write_slowpath
| | |
| | --49.67%--rwsem_optimistic_spin
| | |
| | --49.31%--osq_lock
| |
| --0.74%--up_write
| rwsem_wake.isra.0
| |
| --0.69%--wake_up_q
| |
| --0.62%--try_to_wake_up
| |
|
--0.54%--_raw_spin_lock_irqsave
| |
|
--0.52%--native_queued
|
--29.90%--walk_component
|
--29.72%--lookup_fast
|
--29.51%--kernfs_dop_revalidate
|
|--28.88%--down_read
| |
|
--28.75%--rwsem_down_read_slowpath
| |
|
--28.50%--rwsem_optimistic_spin
| |
|
--28.38%--osq_lock
|
--0.59%--up_read
rwsem_wake.isra.0
|
--0.54%--wake_up_q
|
--0.53%--try_to_wake_up
> Please keep in mind that Greg's continued silence on the question
> of whether the series might be re-considered indicates to me that
> he has not changed his position on this.
Since the problem doesn't break the system, it doesn't need immediate attention.
So I bet it must be labeled with a low priority in Greg's to-do list.
And it's merging
window & holiday season. Let's just give him more time. :)
> ---
>
> Ian Kent (6):
> kernfs: move revalidate to be near lookup
> kernfs: use VFS negative dentry caching
> kernfs: use revision to identify directory node changes
> kernfs: switch kernfs to use an rwsem
> kernfs: stay in rcu-walk mode if possible
> kernfs: add a spinlock to kernfs iattrs for inode updates
>
>
> fs/kernfs/dir.c | 285 ++++++++++++++++++++++++++++---------------
> fs/kernfs/file.c | 4 -
> fs/kernfs/inode.c | 19 ++-
> fs/kernfs/kernfs-internal.h | 30 ++++-
> fs/kernfs/mount.c | 12 +-
> fs/kernfs/symlink.c | 4 -
> include/linux/kernfs.h | 5 +
> 7 files changed, 238 insertions(+), 121 deletions(-)
>
> --
> Ian
>
thanks,
fox
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