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

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

[Stefan Hajnoczi]

The following changes since commit a0def594286d9110a6035e02eef558cf3cf5d847:

  Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging (2017-01-30 10:23:20 +0000)

are available in the git repository at:

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

for you to fetch changes up to 81a9f2cb9336a7e9f50b0729b4c81d287e0015e9:

  iothread: enable AioContext polling by default (2017-01-31 17:09:34 +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 1 February 2017 at 13:24, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> The following changes since commit a0def594286d9110a6035e02eef558cf3cf5d847:
>
>   Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging (2017-01-30 10:23:20 +0000)
>
> are available in the git repository at:
>
>   git://github.com/stefanha/qemu.git block-pull-request
>
> for you to fetch changes up to 81a9f2cb9336a7e9f50b0729b4c81d287e0015e9:
>
>   iothread: enable AioContext polling by default (2017-01-31 17:09:34 +0000)

git claims not to be able to find "block-pull-request",
and https://github.com/stefanha/qemu/tags says it was
pushed 7 days ago with a different commit hash to the
one quoted here. Forgot to tag? Forgot to push?

thanks
-- PMM

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

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 934 bytes --]

On Thu, Feb 02, 2017 at 04:07:16PM +0000, Peter Maydell wrote:
> On 1 February 2017 at 13:24, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > The following changes since commit a0def594286d9110a6035e02eef558cf3cf5d847:
> >
> >   Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging (2017-01-30 10:23:20 +0000)
> >
> > are available in the git repository at:
> >
> >   git://github.com/stefanha/qemu.git block-pull-request
> >
> > for you to fetch changes up to 81a9f2cb9336a7e9f50b0729b4c81d287e0015e9:
> >
> >   iothread: enable AioContext polling by default (2017-01-31 17:09:34 +0000)
> 
> git claims not to be able to find "block-pull-request",
> and https://github.com/stefanha/qemu/tags says it was
> pushed 7 days ago with a different commit hash to the
> one quoted here. Forgot to tag? Forgot to push?

I must have messed something up.

NACK

Will send a fresh pull request.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 455 bytes --]

[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