The original range lock implementation had to be modified by commit
8926ab7 because it was unsafe on Linux. In particular, calling
cv_destroy() immediately after cv_broadcast() is dangerous because
the waiters may still be asleep. Thus the following cv_destroy()
will free memory which may still be in use.
This was fixed by updating cv_destroy() to block on waiters but
this in turn introduced a deadlock. The deadlock was resolved
with the use of a taskq to move the offending free outside the
range lock. This worked well but using the taskq for the free
resulted in a serious performace hit. This is somewhat ironic
because at the time I felt using the taskq might improve things
by making the free asynchronous.
This patch refines the original fix and moves the free from the
taskq to a private free list. Then items which must be free'd
are simply inserted in to the list. When the range lock is dropped
it's safe to free the items. The list is walked and all rl_t
entries are freed.
This change improves small cached read performance by 26x. This
was expected because for small reads the number of locking calls
goes up significantly. More surprisingly this change significantly
improves large cache read performance. This probably attributable
to better cpu/memory locality. Very likely the same processor
which allocated the memory is now freeing it.
bs ext3 zfs zfs+fix faster
----------------------------------------------
512 435 3 79 26x
1k 820 7 160 22x
2k 1536 14 305 21x
4k 2764 28 572 20x
8k 3788 50 1024 20x
16k 4300 86 1843 21x
32k 4505 138 2560 18x
64k 5324 252 3891 15x
128k 5427 276 4710 17x
256k 5427 413 5017 12x
512k 5427 497 5324 10x
1m 5427 521 5632 10x
Closes#142
One of the neat tricks an autoconf style project is capable of
is allow configurion/building in a directory other than the
source directory. The major advantage to this is that you can
build the project various different ways while making changes
in a single source tree.
For example, this project is designed to work on various different
Linux distributions each of which work slightly differently. This
means that changes need to verified on each of those supported
distributions perferably before the change is committed to the
public git repo.
Using nfs and custom build directories makes this much easier.
I now have a single source tree in nfs mounted on several different
systems each running a supported distribution. When I make a
change to the source base I suspect may break things I can
concurrently build from the same source on all the systems each
in their own subdirectory.
wget -c http://github.com/downloads/behlendorf/zfs/zfs-x.y.z.tar.gz
tar -xzf zfs-x.y.z.tar.gz
cd zfs-x-y-z
------------------------- run concurrently ----------------------
<ubuntu system> <fedora system> <debian system> <rhel6 system>
mkdir ubuntu mkdir fedora mkdir debian mkdir rhel6
cd ubuntu cd fedora cd debian cd rhel6
../configure ../configure ../configure ../configure
make make make make
make check make check make check make check
This change also moves many of the include headers from individual
incude/sys directories under the modules directory in to a single
top level include directory. This has the advantage of making
the build rules cleaner and logically it makes a bit more sense.
Brian Behlendorf