[PATCH] reorder struct files_struct
commit95e861db3eaba7bc99f8605db70103ec3d078203
authorEric Dumazet <dada1@cosmosbay.com>
Mon, 14 Nov 2005 00:06:24 +0000 (13 16:06 -0800)
committerLinus Torvalds <torvalds@g5.osdl.org>
Mon, 14 Nov 2005 02:14:10 +0000 (13 18:14 -0800)
tree70f86b1acf1c8b1fb49f8bd11aaf5d81c39d0e97
parentd6c7ac081bf6cafcf780b919ee97978f1d01a0d7
[PATCH] reorder struct files_struct

The file_lock spinlock sits close to mostly read fields of 'struct
files_struct'

In SMP (and NUMA) environments, each time a thread wants to open or close
a file, it has to acquire the spinlock, thus invalidating the cache line
containing this spinlock on other CPUS.  So other threads doing
read()/write()/...  calls that use RCU to access the file table are going
to ask further memory (possibly NUMA) transactions to read again this
memory line.

Move the spinlock to another cache line, so that concurrent threads can
share the cache line containing 'count' and 'fdt' fields.

It's worth up to 9% on a microbenchmark using a 4-thread 2-package x86
machine.  See
http://marc.theaimsgroup.com/?l=linux-kernel&m=112680448713342&w=2

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
include/linux/file.h