linux/include
Linus Torvalds 9226b5b440 vfs: avoid non-forwarding large load after small store in path lookup
The performance regression that Josef Bacik reported in the pathname
lookup (see commit 99d263d4c5 "vfs: fix bad hashing of dentries") made
me look at performance stability of the dcache code, just to verify that
the problem was actually fixed.  That turned up a few other problems in
this area.

There are a few cases where we exit RCU lookup mode and go to the slow
serializing case when we shouldn't, Al has fixed those and they'll come
in with the next VFS pull.

But my performance verification also shows that link_path_walk() turns
out to have a very unfortunate 32-bit store of the length and hash of
the name we look up, followed by a 64-bit read of the combined hash_len
field.  That screws up the processor store to load forwarding, causing
an unnecessary hickup in this critical routine.

It's caused by the ugly calling convention for the "hash_name()"
function, and easily fixed by just making hash_name() fill in the whole
'struct qstr' rather than passing it a pointer to just the hash value.

With that, the profile for this function looks much smoother.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-09-14 17:28:32 -07:00
..
acpi ACPI / scan: not cache _SUN value in struct acpi_device_pnp 2014-09-03 22:41:14 +02:00
asm-generic
clocksource
crypto
drm drm/radeon: add additional SI pci ids 2014-08-22 10:47:59 -04:00
dt-bindings
keys
kvm
linux vfs: avoid non-forwarding large load after small store in path lookup 2014-09-14 17:28:32 -07:00
math-emu
media
memory
misc
net Merge tag 'master-2014-09-04' of git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless 2014-09-07 16:11:10 -07:00
pcmcia
ras
rdma Merge branches 'core', 'cxgb4', 'ipoib', 'iser', 'iwcm', 'mad', 'misc', 'mlx4', 'mlx5', 'ocrdma' and 'srp' into for-next 2014-08-14 08:58:04 -07:00
rxrpc
scsi SCSI misc on 20140815 2014-08-15 18:28:58 -06:00
soc/tegra
sound ASoC: core: fix .info for SND_SOC_BYTES_TLV 2014-08-18 08:59:12 -05:00
target
trace net: treewide: Fix typo found in DocBook/networking.xml 2014-09-05 17:35:28 -07:00
uapi USB fixes for 3.17-rc5 2014-09-12 11:59:10 -07:00
video
xen xen/arm: introduce XENFEAT_grant_map_identity 2014-09-11 18:11:52 +00:00
Kbuild