From ea776cc85615113b780fc6126aa0c7601209cf50 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 [@nathanchance: Leave out documentation, https://github.com/torvalds/linux/commit/8a81252b774b53e628a8a0fe18e2b8fc236d92cc] Signed-off-by: Nathan Chancellor Signed-off-by: Joe Maples --- include/linux/fdtable.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/linux') diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h index 9bf15b13f..cb674d6d6 100644 --- a/include/linux/fdtable.h +++ b/include/linux/fdtable.h @@ -48,6 +48,9 @@ struct files_struct { * read mostly part */ atomic_t count; + bool resize_in_progress; + wait_queue_head_t resize_wait; + struct fdtable __rcu *fdt; struct fdtable fdtab; /* -- cgit v1.2.3