From 8a81252b774b53e628a8a0fe18e2b8fc236d92cc Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 30 Jun 2015 15:54:08 +0200 Subject: 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 Reported-by: Mateusz Guzik Acked-by: Mateusz Guzik Tested-by: Mateusz Guzik Signed-off-by: Al Viro --- Documentation/filesystems/porting | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'Documentation') 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. -- cgit v1.2.3