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Differential D25910

vfs: add VOP_STAT
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Authored by mjg on Aug 1 2020, 8:46 AM.
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rS364044: vfs: add VOP_STAT
Summary

The current scheme of calling VOP_GETATTR adds avoidable overhead.

On Cascade Lake (no meltdown, mds and similar problems) Linux gets the following on tmpfs:
fstat1_processes -t 1 -s 10: average:9299441
fstat1_threads -t 1 -s 10: average:8291153

In contrast, FreeBSD on the same hardware:
fstat1_processes -t 1 -s 10: average:7488958

Patched:
fstat1_processes -t 1 -s 10: average:7913833

[there is no difference for threaded case]

Which mostly catches up to threaded case. Remaining overhead is copying more data and avoidable atomics.

I'll patch other filesystems (zfs and ufs) later.

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rS FreeBSD src repository - subversion
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Event Timeline

mjg created this revision.Aug 1 2020, 8:46 AM
Herald added a subscriber: emaste. · View Herald TranscriptAug 1 2020, 8:46 AM
mjg requested review of this revision.Aug 1 2020, 8:46 AM
mjg edited the summary of this revision. (Show Details)
kib added inline comments.Aug 2 2020, 11:40 PM
sys/fs/tmpfs/tmpfs_vnops.c
458 ↗(On Diff #75242)

Can we avoid having fs to implement both VOP_STAT and VOP_GETATTR if it wants to provide STAT ?

sys/kern/vfs_default.c
1500 ↗(On Diff #75242)

I would argue that post hook should be called regardless of error.

1540 ↗(On Diff #75242)

There

1547 ↗(On Diff #75242)

And there

sys/sys/vnode.h
891 ↗(On Diff #75242)

Why not make them inline functions ?

mjg updated this revision to Diff 75287.Aug 3 2020, 12:23 AM
  • make vop_stat_helper_post mandatory and return an error through it
mjg added inline comments.Aug 3 2020, 12:26 AM
sys/fs/tmpfs/tmpfs_vnops.c
458 ↗(On Diff #75242)

Not right now unfortunately. GETATTR itself is cheaper to execute and called all the time (e.g., mmap). Most consumers are only looking to get the file size though and other cheaply obtainable subset. I had a WIP patch to implement a stripped down GETATTR which provides only what's needed by mmap/exec/lseek/sendfile. With that in place GETATTR itself would be rare enough that we could retire it and indeed create a wrapper around stat.

mjg added inline comments.Aug 3 2020, 12:29 AM
sys/sys/vnode.h
891 ↗(On Diff #75242)

audit and mac add to header mess

mjg updated this revision to Diff 75465.Aug 5 2020, 10:45 PM
  • add manpage
mjg updated this revision to Diff 75467.Aug 5 2020, 11:32 PM
  • better manpage
kib accepted this revision.Aug 6 2020, 1:15 PM
kib added inline comments.
share/man/man9/VOP_ATTRIB.9
56 ↗(On Diff #75467)

I think it would be better to explicitly note that the VOP is optional and should only be provided when such optimization makes sense.

80 ↗(On Diff #75467)

Perhaps this should be marked as result. Same for VOP_GETATTR.

84 ↗(On Diff #75467)

State that NOCRED should be passed if no fd is.

This revision is now accepted and ready to land.Aug 6 2020, 1:15 PM
Closed by commit rS364044: vfs: add VOP_STAT (authored by mjg). · Explain WhyAug 7 2020, 11:07 PM
This revision was automatically updated to reflect the committed changes.
mjg added a commit: rS364044: vfs: add VOP_STAT.
Herald added a reviewer: manpages. · View Herald TranscriptAug 7 2020, 11:07 PM
Herald added a subscriber: imp. · View Herald Transcript

Revision Contents
Changeset List

PathSize
head/
share/
man/
man9/
3 lines
45 lines
sys/
compat/
linuxkpi/
common/
src/
2 lines
kern/
113 lines
6 lines
113 lines
11 lines
security/
audit/
2 lines
sys/
18 lines

Diff 75595

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head/share/man/man9/Makefile

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head/share/man/man9/VOP_ATTRIB.9

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head/sys/compat/linuxkpi/common/src/linux_compat.c

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head/sys/kern/vfs_default.c

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head/sys/kern/vfs_syscalls.c

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head/sys/kern/vfs_vnops.c

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head/sys/kern/vnode_if.src

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head/sys/security/audit/audit_arg.c

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head/sys/sys/vnode.h

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