[Qemu-devel] [PULL 1/1] iothread: enable AioContext polling by default

[Qemu-devel] [PULL 1/1] iothread: enable AioContext polling by default

[Stefan Hajnoczi]

IOThread AioContexts are likely to consist only of event sources like
virtqueue ioeventfds and LinuxAIO completion eventfds that are pollable
from userspace (without system calls).

We recently merged the AioContext polling feature but didn't enable it
by default yet.  I have gone back over the performance data on the
mailing list and picked a default polling value that gave good results.

Let's enable AioContext polling by default so users don't have another
switch they need to set manually.  If performance regressions are found
we can still disable this for the QEMU 2.9 release.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Karl Rister <krister@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20170126170119.27876-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 iothread.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/iothread.c b/iothread.c
index 7bedde8..257b01d 100644
--- a/iothread.c
+++ b/iothread.c
@@ -30,6 +30,12 @@ typedef ObjectClass IOThreadClass;
 #define IOTHREAD_CLASS(klass) \
    OBJECT_CLASS_CHECK(IOThreadClass, klass, TYPE_IOTHREAD)
 
+/* Benchmark results from 2016 on NVMe SSD drives show max polling times around
+ * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32
+ * workloads.
+ */
+#define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL
+
 static __thread IOThread *my_iothread;
 
 AioContext *qemu_get_current_aio_context(void)
@@ -71,6 +77,13 @@ static int iothread_stop(Object *object, void *opaque)
     return 0;
 }
 
+static void iothread_instance_init(Object *obj)
+{
+    IOThread *iothread = IOTHREAD(obj);
+
+    iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT;
+}
+
 static void iothread_instance_finalize(Object *obj)
 {
     IOThread *iothread = IOTHREAD(obj);
@@ -215,6 +228,7 @@ static const TypeInfo iothread_info = {
     .parent = TYPE_OBJECT,
     .class_init = iothread_class_init,
     .instance_size = sizeof(IOThread),
+    .instance_init = iothread_instance_init,
     .instance_finalize = iothread_instance_finalize,
     .interfaces = (InterfaceInfo[]) {
         {TYPE_USER_CREATABLE},
-- 
2.9.3

[Qemu-devel] [PULL 0/1] Block patches

[Stefan Hajnoczi]

The following changes since commit 4100a344eb3d50d88f9da85cae334afc47aee134:

  Merge remote-tracking branch 'remotes/sstabellini/tags/xen-20170202' into staging (2017-02-03 12:31:40 +0000)

are available in the git repository at:

  git://github.com/stefanha/qemu.git tags/block-pull-request

for you to fetch changes up to cdd7abfdba9287a289c404dfdcb02316f9ffee7d:

  iothread: enable AioContext polling by default (2017-02-03 14:23:38 +0000)

----------------------------------------------------------------

----------------------------------------------------------------

Stefan Hajnoczi (1):
  iothread: enable AioContext polling by default

 iothread.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

-- 
2.9.3

[Qemu-devel] [PULL 1/1] iothread: enable AioContext polling by default

[Stefan Hajnoczi]

IOThread AioContexts are likely to consist only of event sources like
virtqueue ioeventfds and LinuxAIO completion eventfds that are pollable
from userspace (without system calls).

We recently merged the AioContext polling feature but didn't enable it
by default yet.  I have gone back over the performance data on the
mailing list and picked a default polling value that gave good results.

Let's enable AioContext polling by default so users don't have another
switch they need to set manually.  If performance regressions are found
we can still disable this for the QEMU 2.9 release.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Karl Rister <krister@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20170126170119.27876-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 iothread.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/iothread.c b/iothread.c
index 7bedde8..257b01d 100644
--- a/iothread.c
+++ b/iothread.c
@@ -30,6 +30,12 @@ typedef ObjectClass IOThreadClass;
 #define IOTHREAD_CLASS(klass) \
    OBJECT_CLASS_CHECK(IOThreadClass, klass, TYPE_IOTHREAD)
 
+/* Benchmark results from 2016 on NVMe SSD drives show max polling times around
+ * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32
+ * workloads.
+ */
+#define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL
+
 static __thread IOThread *my_iothread;
 
 AioContext *qemu_get_current_aio_context(void)
@@ -71,6 +77,13 @@ static int iothread_stop(Object *object, void *opaque)
     return 0;
 }
 
+static void iothread_instance_init(Object *obj)
+{
+    IOThread *iothread = IOTHREAD(obj);
+
+    iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT;
+}
+
 static void iothread_instance_finalize(Object *obj)
 {
     IOThread *iothread = IOTHREAD(obj);
@@ -215,6 +228,7 @@ static const TypeInfo iothread_info = {
     .parent = TYPE_OBJECT,
     .class_init = iothread_class_init,
     .instance_size = sizeof(IOThread),
+    .instance_init = iothread_instance_init,
     .instance_finalize = iothread_instance_finalize,
     .interfaces = (InterfaceInfo[]) {
         {TYPE_USER_CREATABLE},
-- 
2.9.3

Re: [Qemu-devel] [PULL 0/1] Block patches

[Peter Maydell]

On 3 February 2017 at 14:37, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> The following changes since commit 4100a344eb3d50d88f9da85cae334afc47aee134:
>
>   Merge remote-tracking branch 'remotes/sstabellini/tags/xen-20170202' into staging (2017-02-03 12:31:40 +0000)
>
> are available in the git repository at:
>
>   git://github.com/stefanha/qemu.git tags/block-pull-request
>
> for you to fetch changes up to cdd7abfdba9287a289c404dfdcb02316f9ffee7d:
>
>   iothread: enable AioContext polling by default (2017-02-03 14:23:38 +0000)
>
> ----------------------------------------------------------------
>
> ----------------------------------------------------------------

Applied, thanks.

-- PMM