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| author | Stefan Hajnoczi <stefanha@redhat.com> | 2020-03-05 17:08:01 +0000 |
|---|---|---|
| committer | Stefan Hajnoczi <stefanha@redhat.com> | 2020-03-09 16:41:31 +0000 |
| commit | 3aa221b382c9b36db1750ef5ed340b6566aacb8c (patch) | |
| tree | bdc6ceb75661f05b66ab4b77e9a4a59c0da1e490 /util | |
| parent | e4346192f1c2e1683a807b46efac47ef0cf9b545 (diff) | |
| download | qemu-3aa221b382c9b36db1750ef5ed340b6566aacb8c.zip qemu-3aa221b382c9b36db1750ef5ed340b6566aacb8c.tar.gz qemu-3aa221b382c9b36db1750ef5ed340b6566aacb8c.tar.bz2 | |
aio-posix: move RCU_READ_LOCK() into run_poll_handlers()
Now that run_poll_handlers_once() is only called by run_poll_handlers()
we can improve the CPU time profile by moving the expensive
RCU_READ_LOCK() out of the polling loop.
This reduces the run_poll_handlers() from 40% CPU to 10% CPU in perf's
sampling profiler output.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Link: https://lore.kernel.org/r/20200305170806.1313245-3-stefanha@redhat.com
Message-Id: <20200305170806.1313245-3-stefanha@redhat.com>
Diffstat (limited to 'util')
| -rw-r--r-- | util/aio-posix.c | 20 |
1 files changed, 10 insertions, 10 deletions
diff --git a/util/aio-posix.c b/util/aio-posix.c index 65964a2..11a4971 100644 --- a/util/aio-posix.c +++ b/util/aio-posix.c @@ -583,16 +583,6 @@ static bool run_poll_handlers_once(AioContext *ctx, int64_t *timeout) bool progress = false; AioHandler *node; - /* - * Optimization: ->io_poll() handlers often contain RCU read critical - * sections and we therefore see many rcu_read_lock() -> rcu_read_unlock() - * -> rcu_read_lock() -> ... sequences with expensive memory - * synchronization primitives. Make the entire polling loop an RCU - * critical section because nested rcu_read_lock()/rcu_read_unlock() calls - * are cheap. - */ - RCU_READ_LOCK_GUARD(); - QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) { if (!QLIST_IS_INSERTED(node, node_deleted) && node->io_poll && aio_node_check(ctx, node->is_external) && @@ -636,6 +626,16 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout) trace_run_poll_handlers_begin(ctx, max_ns, *timeout); + /* + * Optimization: ->io_poll() handlers often contain RCU read critical + * sections and we therefore see many rcu_read_lock() -> rcu_read_unlock() + * -> rcu_read_lock() -> ... sequences with expensive memory + * synchronization primitives. Make the entire polling loop an RCU + * critical section because nested rcu_read_lock()/rcu_read_unlock() calls + * are cheap. + */ + RCU_READ_LOCK_GUARD(); + start_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); do { progress = run_poll_handlers_once(ctx, timeout); |