[Qemu-devel] [PATCH v3 0/2] dataplane: add query-iothreads QMP command

[Qemu-devel] [PATCH v3 0/2] dataplane: add query-iothreads QMP command

[Stefan Hajnoczi]

v3:
 * Loop until predicate is true to handle pthread_cond spurious wakeups [eblake]
 * Fix additional instances of "thread_id" [eblake]

v2:
 * Use "thread-id" instead of "thread_id" in QAPI [eblake]
 * Avoid mutex unlock/destroy race between threads [pbonzini]

This series applies on top of "[PATCH v4 0/6] dataplane: switch to N:M
devices-per-thread model".

The new "query-iothreads" command allows QMP clients to fetch the thread IDs
for dataplane threads.  This will allow libvirt and friends to bind dataplane
threads.

The approach is similar to "query-cpus" which is also used for vcpu thread
binding (among other things).

Stefan Hajnoczi (2):
  iothread: stash thread ID away
  qmp: add query-iothreads command

 iothread.c       | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 qapi-schema.json | 29 ++++++++++++++++++++++++++++
 qmp-commands.hx  | 39 +++++++++++++++++++++++++++++++++++++
 3 files changed, 126 insertions(+)

-- 
1.8.5.3

[Qemu-devel] [PATCH v3 1/2] iothread: stash thread ID away

[Stefan Hajnoczi]

Keep the thread ID around so we can report it via QMP.

There's only one problem: qemu_get_thread_id() (gettid() wrapper on
Linux) must be called from the thread itself.  There is no way to get
the thread ID outside the thread.

This patch uses a condvar to wait for iothread_run() to populate the
thread_id inside the thread.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 iothread.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/iothread.c b/iothread.c
index 033de7f..0a3c048 100644
--- a/iothread.c
+++ b/iothread.c
@@ -25,7 +25,10 @@ struct IOThread {
     Object parent;
     QemuThread thread;
     AioContext *ctx;
+    QemuMutex init_done_lock;
+    QemuCond init_done_cond;    /* is thread initialization done? */
     bool stopping;
+    int thread_id;
 };
 
 #define IOTHREAD_GET_CLASS(obj) \
@@ -37,6 +40,11 @@ static void *iothread_run(void *opaque)
 {
     IOThread *iothread = opaque;
 
+    qemu_mutex_lock(&iothread->init_done_lock);
+    iothread->thread_id = qemu_get_thread_id();
+    qemu_cond_signal(&iothread->init_done_cond);
+    qemu_mutex_unlock(&iothread->init_done_lock);
+
     while (!iothread->stopping) {
         aio_context_acquire(iothread->ctx);
         while (!iothread->stopping && aio_poll(iothread->ctx, true)) {
@@ -54,6 +62,8 @@ static void iothread_instance_finalize(Object *obj)
     iothread->stopping = true;
     aio_notify(iothread->ctx);
     qemu_thread_join(&iothread->thread);
+    qemu_cond_destroy(&iothread->init_done_cond);
+    qemu_mutex_destroy(&iothread->init_done_lock);
     aio_context_unref(iothread->ctx);
 }
 
@@ -63,12 +73,24 @@ static void iothread_complete(UserCreatable *obj, Error **errp)
 
     iothread->stopping = false;
     iothread->ctx = aio_context_new();
+    iothread->thread_id = -1;
+
+    qemu_mutex_init(&iothread->init_done_lock);
+    qemu_cond_init(&iothread->init_done_cond);
 
     /* This assumes we are called from a thread with useful CPU affinity for us
      * to inherit.
      */
     qemu_thread_create(&iothread->thread, iothread_run,
                        iothread, QEMU_THREAD_JOINABLE);
+
+    /* Wait for initialization to complete */
+    qemu_mutex_lock(&iothread->init_done_lock);
+    while (iothread->thread_id == -1) {
+        qemu_cond_wait(&iothread->init_done_cond,
+                       &iothread->init_done_lock);
+    }
+    qemu_mutex_unlock(&iothread->init_done_lock);
 }
 
 static void iothread_class_init(ObjectClass *klass, void *class_data)
-- 
1.8.5.3

[Qemu-devel] [PATCH v3 2/2] qmp: add query-iothreads command

[Stefan Hajnoczi]

The "query-iothreads" command returns a list of information about
iothreads.  See the patch for API documentation.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 iothread.c       | 36 ++++++++++++++++++++++++++++++++++++
 qapi-schema.json | 29 +++++++++++++++++++++++++++++
 qmp-commands.hx  | 39 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 104 insertions(+)

diff --git a/iothread.c b/iothread.c
index 0a3c048..e348706 100644
--- a/iothread.c
+++ b/iothread.c
@@ -17,6 +17,7 @@
 #include "qemu/thread.h"
 #include "block/aio.h"
 #include "sysemu/iothread.h"
+#include "qmp-commands.h"
 
 #define IOTHREADS_PATH "/objects"
 
@@ -143,3 +144,38 @@ AioContext *iothread_get_aio_context(IOThread *iothread)
 {
     return iothread->ctx;
 }
+
+static int query_one_iothread(Object *object, void *opaque)
+{
+    IOThreadInfoList ***prev = opaque;
+    IOThreadInfoList *elem;
+    IOThreadInfo *info;
+    IOThread *iothread;
+
+    iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
+    if (!iothread) {
+        return 0;
+    }
+
+    info = g_new0(IOThreadInfo, 1);
+    info->id = iothread_get_id(iothread);
+    info->thread_id = iothread->thread_id;
+
+    elem = g_new0(IOThreadInfoList, 1);
+    elem->value = info;
+    elem->next = NULL;
+
+    **prev = elem;
+    *prev = &elem->next;
+    return 0;
+}
+
+IOThreadInfoList *qmp_query_iothreads(Error **errp)
+{
+    IOThreadInfoList *head = NULL;
+    IOThreadInfoList **prev = &head;
+    Object *container = container_get(object_get_root(), IOTHREADS_PATH);
+
+    object_child_foreach(container, query_one_iothread, &prev);
+    return head;
+}
diff --git a/qapi-schema.json b/qapi-schema.json
index ac8ad24..9888418 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -883,6 +883,35 @@
 { 'command': 'query-cpus', 'returns': ['CpuInfo'] }
 
 ##
+# @IOThreadInfo:
+#
+# Information about an iothread
+#
+# @id: the identifier of the iothread
+#
+# @thread-id: ID of the underlying host thread
+#
+# Since: 2.0
+##
+{ 'type': 'IOThreadInfo',
+  'data': {'id': 'str', 'thread-id': 'int'} }
+
+##
+# @query-iothreads:
+#
+# Returns a list of information about each iothread.
+#
+# Note this list excludes the QEMU main loop thread, which is not declared
+# using the -object iothread command-line option.  It is always the main thread
+# of the process.
+#
+# Returns: a list of @IOThreadInfo for each iothread
+#
+# Since: 2.0
+##
+{ 'command': 'query-iothreads', 'returns': ['IOThreadInfo'] }
+
+##
 # @BlockDeviceInfo:
 #
 # Information about the backing device for a block device.
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 8a0e832..f3407da 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -2304,6 +2304,45 @@ EQMP
     },
 
 SQMP
+query-iothreads
+---------------
+
+Returns a list of information about each iothread.
+
+Note this list excludes the QEMU main loop thread, which is not declared
+using the -object iothread command-line option.  It is always the main thread
+of the process.
+
+Return a json-array. Each iothread is represented by a json-object, which contains:
+
+- "id": name of iothread (json-str)
+- "thread-id": ID of the underlying host thread (json-int)
+
+Example:
+
+-> { "execute": "query-iothreads" }
+<- {
+      "return":[
+         {
+            "id":"iothread0",
+            "thread-id":3134
+         },
+         {
+            "id":"iothread1",
+            "thread-id":3135
+         }
+      ]
+   }
+
+EQMP
+
+    {
+        .name       = "query-iothreads",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_input_query_iothreads,
+    },
+
+SQMP
 query-pci
 ---------
 
-- 
1.8.5.3

Re: [Qemu-devel] [PATCH v3 0/2] dataplane: add query-iothreads QMP command

[Eric Blake]

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On 02/27/2014 03:48 AM, Stefan Hajnoczi wrote:
> v3:
>  * Loop until predicate is true to handle pthread_cond spurious wakeups [eblake]
>  * Fix additional instances of "thread_id" [eblake]
> 
> v2:
>  * Use "thread-id" instead of "thread_id" in QAPI [eblake]
>  * Avoid mutex unlock/destroy race between threads [pbonzini]
> 
> This series applies on top of "[PATCH v4 0/6] dataplane: switch to N:M
> devices-per-thread model".

Series: Reviewed-by: Eric Blake <eblake@redhat.com>

> 
> The new "query-iothreads" command allows QMP clients to fetch the thread IDs
> for dataplane threads.  This will allow libvirt and friends to bind dataplane
> threads.
> 
> The approach is similar to "query-cpus" which is also used for vcpu thread
> binding (among other things).
> 
> Stefan Hajnoczi (2):
>   iothread: stash thread ID away
>   qmp: add query-iothreads command
> 
>  iothread.c       | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  qapi-schema.json | 29 ++++++++++++++++++++++++++++
>  qmp-commands.hx  | 39 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 126 insertions(+)
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH v3 0/2] dataplane: add query-iothreads QMP command

[Luiz Capitulino]

On Thu, 27 Feb 2014 11:48:40 +0100
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> v3:
>  * Loop until predicate is true to handle pthread_cond spurious wakeups [eblake]
>  * Fix additional instances of "thread_id" [eblake]
> 
> v2:
>  * Use "thread-id" instead of "thread_id" in QAPI [eblake]
>  * Avoid mutex unlock/destroy race between threads [pbonzini]
> 
> This series applies on top of "[PATCH v4 0/6] dataplane: switch to N:M
> devices-per-thread model".

What's the merge plan for both series? IMO, they should go in through the
block layer tree. As far as the QMP interface is concerned, Eric's review is
all you need.

> 
> The new "query-iothreads" command allows QMP clients to fetch the thread IDs
> for dataplane threads.  This will allow libvirt and friends to bind dataplane
> threads.
> 
> The approach is similar to "query-cpus" which is also used for vcpu thread
> binding (among other things).
> 
> Stefan Hajnoczi (2):
>   iothread: stash thread ID away
>   qmp: add query-iothreads command
> 
>  iothread.c       | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  qapi-schema.json | 29 ++++++++++++++++++++++++++++
>  qmp-commands.hx  | 39 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 126 insertions(+)
> 

Re: [Qemu-devel] [PATCH v3 0/2] dataplane: add query-iothreads QMP command

[Stefan Hajnoczi]

On Fri, Feb 28, 2014 at 02:00:28PM -0500, Luiz Capitulino wrote:
> On Thu, 27 Feb 2014 11:48:40 +0100
> Stefan Hajnoczi <stefanha@redhat.com> wrote:
> 
> > v3:
> >  * Loop until predicate is true to handle pthread_cond spurious wakeups [eblake]
> >  * Fix additional instances of "thread_id" [eblake]
> > 
> > v2:
> >  * Use "thread-id" instead of "thread_id" in QAPI [eblake]
> >  * Avoid mutex unlock/destroy race between threads [pbonzini]
> > 
> > This series applies on top of "[PATCH v4 0/6] dataplane: switch to N:M
> > devices-per-thread model".
> 
> What's the merge plan for both series? IMO, they should go in through the
> block layer tree. As far as the QMP interface is concerned, Eric's review is
> all you need.

Okay, thanks.

They can go through Kevin if he's ready to merge them this week, or me
next week otherwise.

Stefan

Re: [Qemu-devel] [PATCH v3 0/2] dataplane: add query-iothreads QMP command

[Stefan Hajnoczi]

On Thu, Feb 27, 2014 at 11:48:40AM +0100, Stefan Hajnoczi wrote:
> v3:
>  * Loop until predicate is true to handle pthread_cond spurious wakeups [eblake]
>  * Fix additional instances of "thread_id" [eblake]
> 
> v2:
>  * Use "thread-id" instead of "thread_id" in QAPI [eblake]
>  * Avoid mutex unlock/destroy race between threads [pbonzini]
> 
> This series applies on top of "[PATCH v4 0/6] dataplane: switch to N:M
> devices-per-thread model".
> 
> The new "query-iothreads" command allows QMP clients to fetch the thread IDs
> for dataplane threads.  This will allow libvirt and friends to bind dataplane
> threads.
> 
> The approach is similar to "query-cpus" which is also used for vcpu thread
> binding (among other things).
> 
> Stefan Hajnoczi (2):
>   iothread: stash thread ID away
>   qmp: add query-iothreads command
> 
>  iothread.c       | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  qapi-schema.json | 29 ++++++++++++++++++++++++++++
>  qmp-commands.hx  | 39 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 126 insertions(+)

Applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan