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| author | Eric Dumazet <edumazet@google.com> | 2015-06-30 15:54:08 +0200 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2015-07-01 02:30:09 -0400 |
| commit | 8a81252b774b53e628a8a0fe18e2b8fc236d92cc (patch) | |
| tree | 2176cd782e2b578da7ac1072f4430bf68e22c274 /Documentation | |
| parent | 1af95de6f0119d5bde02d3a811a9f3a3661e954e (diff) | |
| download | linux-8a81252b774b53e628a8a0fe18e2b8fc236d92cc.tar.gz linux-8a81252b774b53e628a8a0fe18e2b8fc236d92cc.tar.bz2 linux-8a81252b774b53e628a8a0fe18e2b8fc236d92cc.zip | |
fs/file.c: don't acquire files->file_lock in fd_install()
Mateusz Guzik reported :
Currently obtaining a new file descriptor results in locking fdtable
twice - once in order to reserve a slot and second time to fill it.
Holding the spinlock in __fd_install() is needed in case a resize is
done, or to prevent a resize.
Mateusz provided an RFC patch and a micro benchmark :
http://people.redhat.com/~mguzik/pipebench.c
A resize is an unlikely operation in a process lifetime,
as table size is at least doubled at every resize.
We can use RCU instead of the spinlock.
__fd_install() must wait if a resize is in progress.
The resize must block new __fd_install() callers from starting,
and wait that ongoing install are finished (synchronize_sched())
resize should be attempted by a single thread to not waste resources.
rcu_sched variant is used, as __fd_install() and expand_fdtable() run
from process context.
It gives us a ~30% speedup using pipebench on a dual Intel(R) Xeon(R)
CPU E5-2696 v2 @ 2.50GHz
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Mateusz Guzik <mguzik@redhat.com>
Acked-by: Mateusz Guzik <mguzik@redhat.com>
Tested-by: Mateusz Guzik <mguzik@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/filesystems/porting | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting index 3eae250254d5..ec5456113072 100644 --- a/Documentation/filesystems/porting +++ b/Documentation/filesystems/porting @@ -500,3 +500,7 @@ in your dentry operations instead. dentry, it does not get nameidata at all and it gets called only when cookie is non-NULL. Note that link body isn't available anymore, so if you need it, store it as cookie. +-- +[mandatory] + __fd_install() & fd_install() can now sleep. Callers should not + hold a spinlock or other resources that do not allow a schedule. |