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mark alloc_fd with EXPORT_SYMBOL so it can be used by modules.
Change-Id: Ic0dedbadecd2d0937cad8268aaa6eabbc52019ff
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
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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>
[@nathanchance: Leave out documentation, https://github.com/torvalds/linux/commit/8a81252b774b53e628a8a0fe18e2b8fc236d92cc]
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Joe Maples <joe@frap129.org>
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We clear the close-on-exec flag when opening and closing files, and the
bit was almost always already clear before. Avoid dirtying the
cacheline if the clearning isn't necessary. That avoids unnecessary
cacheline dirtying and bouncing in multi-socket environments.
Eric Dumazet has a file descriptor benchmark that goes 4% faster from
this on his two-socket machine. It's probably partly superlinear
improvement due to getting slightly less spinlock contention on the
file_lock spinlock due to less work in the critical section.
Tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: Joe Maples <joe@frap129.org>
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Al Viro points out that:
> > * [Linux-specific aside] our __alloc_fd() can degrade quite badly
> > with some use patterns. The cacheline pingpong in the bitmap is probably
> > inevitable, unless we accept considerably heavier memory footprint,
> > but we also have a case when alloc_fd() takes O(n) and it's _not_ hard
> > to trigger - close(3);open(...); will have the next open() after that
> > scanning the entire in-use bitmap.
And Eric Dumazet has a somewhat realistic multithreaded microbenchmark
that opens and closes a lot of sockets with minimal work per socket.
This patch largely fixes it. We keep a 2nd-level bitmap of the open
file bitmaps, showing which words are already full. So then we can
traverse that second-level bitmap to efficiently skip already allocated
file descriptors.
On his benchmark, this improves performance by up to an order of
magnitude, by avoiding the excessive open file bitmap scanning.
Tested-and-acked-by: Eric Dumazet <edumazet@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: Joe Maples <joe@frap129.org>
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