[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-block] [Qemu-stable] [PATCH for-2.9] thread-pool: add missing

From: Peter Lieven
Subject: Re: [Qemu-block] [Qemu-stable] [PATCH for-2.9] thread-pool: add missing qemu_bh_cancel in completion function
Date: Thu, 16 Mar 2017 21:24:20 +0100

Am 16.03.2017 um 17:18 schrieb Paolo Bonzini <address@hidden>:

On 16/03/2017 17:02, Peter Lieven wrote:
commit 3c80ca15 fixed a deadlock scenarion with nested aio_poll invocations.

However, the rescheduling of the completion BH introcuded unnecessary spinning
in the main-loop. On very fast file backends this can even lead to the
"WARNING: I/O thread spun for 1000 iterations" message popping up.

Callgrind reports about 3-4% less instructions with this patch running
qemu-img bench on a ramdisk based VMDK file.

Fixes: 3c80ca158c96ff902a30883a8933e755988948b1
Cc: address@hidden
Signed-off-by: Peter Lieven <address@hidden>
util/thread-pool.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/util/thread-pool.c b/util/thread-pool.c
index ce6cd30..610646d 100644
--- a/util/thread-pool.c
+++ b/util/thread-pool.c
@@ -188,6 +188,13 @@ restart:
            elem->common.cb(elem->common.opaque, elem->ret);
+            /* We can safely cancel the completion_bh here regardless of someone
+             * else having scheduled it meanwhile because we reenter the
+             * completion function anyway (goto restart).
+             */
+            qemu_bh_cancel(pool->completion_bh);
            goto restart;
        } else {

Right, this is the same thing that block/linux-aio.c does.

Okay, so you also think its safe to do this? As far as I have seen you have been working a lot on the aio code recently.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]