DragonFly commits List (threaded) for 2011-07
git: HAMMER VFS - Add code to reduce frontend vs flusher locking conflicts
Author: Matthew Dillon <email@example.com>
Date: Fri Jul 22 08:55:06 2011 -0700
HAMMER VFS - Add code to reduce frontend vs flusher locking conflicts
* Implement a Pulse-width modulated time-domain multiplexer on B-Tree
cursor operations which splits fronttend operations from backend flusher
The larger the number of inodes undergoing reclamation, the greater the
pulse width given over to locking operations initiated by the flusher.
Frontend operations (typically reads) are given smaller and smaller
slot widths as the flusher gets more overloaded.
The advantage of this mechanism is that we are not simply imposing a
delay in the reader, we are imposing a variable-length time slot during
which the reader is able to grab a B-Tree cursor. This allows linear
and partially cached operations to 'burst' many operations within the
slot, allowing them run at nearly full speed and not imposing an artificial
performance limitation for linear I/O.
* This solves a major deadlock stalling issue that prevented the flusher
from being able to actually flush sufficient I/O to keep up with the
inode backlog that e.g. blogbench creates, causing excessive locking
stalls throughout the HAMMER filesystem, particularly when many file
inodes are being cycled through.
* When running blogbench --iterations=150 prior to this change write
performance would drop to unacceptable levels and read operations
(particularly things which cycle through inodes like 'find' and 'ls')
would stall for unacceptably long periods of time, often resulting
in diagnostic cache_lock messages on the console showing namecache
blockages in excess of 100 seconds.
With the change namecache blockages are significantly reduced in both
frequency and duration, find and ls operations are able to run
concurrently with a heavy multi-file write load, and blogbench shows
improved write performance while still giving a reasonable priority to
read operations (which is what we want).
* Rename a few of the sysctls to normalize internal vs external variable
Summary of changes:
sys/vfs/hammer/hammer.h | 11 ++-
sys/vfs/hammer/hammer_cursor.c | 166 +++++++++++++++++++++++++++++++++++++-
sys/vfs/hammer/hammer_flusher.c | 117 +++++++++++----------------
sys/vfs/hammer/hammer_inode.c | 36 +++++----
sys/vfs/hammer/hammer_vfsops.c | 31 ++++++--
5 files changed, 259 insertions(+), 102 deletions(-)
DragonFly BSD source repository