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Alex Bennée a890643958 util/qht: atomically set b->hashes 
ThreadSanitizer detects a possible race between reading/writing the
hashes. The ordering semantics are already documented for QHT however
for true C11 compliance we should use relaxed atomic primitives for
accesses that are done across threads. On x86 this slightly changes to
the code to not do a load/compare in a single instruction leading to a
slight performance degradation.

Running 'taskset -c 0 tests/qht-bench -n 1 -d 10' (i.e. all lookups) 10
times, we get:

before the patch:
 $ ./mean.pl 34.04 34.24 34.38 34.25 34.18 34.51 34.46 34.44 34.29 34.08
 34.287 +- 0.160072900059109
after:
 $ ./mean.pl 33.94 34.00 33.52 33.46 33.55 33.71 34.27 34.06 34.28 34.58
 33.937 +- 0.374731014640279

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Emilio G. Cota <cota@braap.org>
Message-Id: <20160930213106.20186-10-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
 		2016-10-04 10:00:26 +02:00
..
Makefile.objs util: Add UUID API 2016-09-23 11:42:52 +08:00
acl.c Drop Emacs local variables lists redundant with .dir-locals.el 2016-07-12 16:19:16 +02:00
base64.c include/qemu/osdep.h: Don't include qapi/error.h 2016-03-22 22:20:15 +01:00
bitmap.c util: Clean up includes 2016-02-04 17:01:04 +00:00
bitops.c util: Clean up includes 2016-02-04 17:01:04 +00:00
buffer.c qemu-common: stop including qemu/host-utils.h from qemu-common.h 2016-05-19 16:42:28 +02:00
bufferiszero.c cutils: Rewrite x86 buffer zero checking 2016-09-14 12:25:14 +02:00
compatfd.c util: Clean up includes 2016-02-04 17:01:04 +00:00
coroutine-gthread.c all: Remove unnecessary glib.h includes 2016-06-07 18:19:24 +03:00
coroutine-sigaltstack.c Remove unneeded include statements for setjmp.h 2016-03-22 19:11:15 +01:00
coroutine-ucontext.c Remove unneeded include statements for setjmp.h 2016-03-22 19:11:15 +01:00
coroutine-win32.c util: Clean up includes 2016-02-04 17:01:04 +00:00
crc32c.c util: Clean up includes 2016-02-04 17:01:04 +00:00
cutils.c cutils: Move buffer_is_zero and subroutines to a new file 2016-09-13 19:09:45 +02:00
envlist.c util: Clean up includes 2016-02-04 17:01:04 +00:00
error.c migration: add reporting of errors for outgoing migration 2016-05-26 11:31:30 +05:30
event_notifier-posix.c event-notifier: Add "is_external" parameter 2016-04-22 16:43:56 +02:00
event_notifier-win32.c event-notifier: Add "is_external" parameter 2016-04-22 16:43:56 +02:00
fifo8.c util: Clean up includes 2016-02-04 17:01:04 +00:00
getauxval.c util: Clean up includes 2016-02-04 17:01:04 +00:00
hbitmap.c hbitmap: add 'pos < size' asserts 2016-06-16 15:20:37 +02:00
hexdump.c util: Improved qemu_hexmap() to include an ascii dump of the buffer 2016-04-06 09:52:07 +08:00
host-utils.c util: Clean up includes 2016-02-04 17:01:04 +00:00
id.c util: move declarations out of qemu-common.h 2016-03-22 22:20:17 +01:00
iov.c util: Fix assertion in iov_copy() upon zero 'bytes' and non-zero 'offset' 2016-08-03 18:44:57 +02:00
log.c log: fix parsing of multiple trace:PATTERN log args 2016-09-14 22:52:44 +02:00
memfd.c os-posix: include sys/mman.h 2016-06-16 18:39:03 +02:00
mmap-alloc.c Use #include "..." for our own headers, <...> for others 2016-07-12 16:19:16 +02:00
module.c blockdev: Add dynamic module loading for block drivers 2016-09-20 22:12:03 +02:00
notify.c util: Clean up includes 2016-02-04 17:01:04 +00:00
osdep.c osdep: Introduce qemu_dup 2016-07-13 13:26:02 +02:00
oslib-posix.c fix qemu exit on memory hotplug when allocation fails at prealloc time 2016-08-02 12:03:58 +02:00
oslib-win32.c fix qemu exit on memory hotplug when allocation fails at prealloc time 2016-08-02 12:03:58 +02:00
path.c util: move declarations out of qemu-common.h 2016-03-22 22:20:17 +01:00
qdist.c qdist: return "(empty)" instead of NULL when printing an empty dist 2016-08-03 18:44:56 +02:00
qemu-config.c util: Clean up includes 2016-02-04 17:01:04 +00:00
qemu-coroutine-io.c coroutine: move entry argument to qemu_coroutine_create 2016-07-13 13:26:02 +02:00
qemu-coroutine-lock.c coroutine: Assert that no locks are held on termination 2016-09-05 19:06:48 +02:00
qemu-coroutine-sleep.c coroutine: move entry argument to qemu_coroutine_create 2016-07-13 13:26:02 +02:00
qemu-coroutine.c coroutine: add qemu_coroutine_entered() function 2016-09-28 17:11:23 +01:00
qemu-error.c util: Clean up includes 2016-02-04 17:01:04 +00:00
qemu-openpty.c util: Clean up includes 2016-02-04 17:01:04 +00:00
qemu-option.c QemuOpts: Fix qemu_opts_foreach() dangling location regression 2016-04-28 08:18:56 +02:00
qemu-progress.c util: Clean up includes 2016-02-04 17:01:04 +00:00
qemu-sockets.c util: fix some coding style issue 2016-09-13 19:08:42 +02:00
qemu-thread-posix.c util: Clean up includes 2016-02-04 17:01:04 +00:00
qemu-thread-win32.c util: Clean up includes 2016-02-04 17:01:04 +00:00
qemu-timer-common.c util: Clean up includes 2016-02-04 17:01:04 +00:00
qht.c util/qht: atomically set b->hashes 2016-10-04 10:00:26 +02:00
range.c range: Replace internal representation of Range 2016-07-04 16:49:33 +03:00
rcu.c util: Clean up includes 2016-02-04 17:01:04 +00:00
readline.c util: move declarations out of qemu-common.h 2016-03-22 22:20:17 +01:00
rfifolock.c rfifolock: no need to get thread identifier when nesting 2016-05-16 15:29:44 -07:00
throttle.c throttle: Don't allow burst limits to be lower than the normal limits 2016-08-05 09:59:06 +01:00
timed-average.c Fix some typos found by codespell 2016-05-18 15:04:27 +03:00
trace-events trace: move util/qemu-coroutine*.c trace points into correct file 2016-09-28 19:17:54 +01:00
unicode.c util: move declarations out of qemu-common.h 2016-03-22 22:20:17 +01:00
uri.c all: Remove unnecessary glib.h includes 2016-06-07 18:19:24 +03:00
uuid.c uuid: Tighten uuid parse 2016-09-23 11:42:52 +08:00