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Re: [Qemu-devel] [PATCH 9/9] dataplane: use a QContext event loop in pla
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 9/9] dataplane: use a QContext event loop in place of custom thread |
Date: |
Mon, 06 May 2013 09:54:03 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
Il 03/05/2013 18:03, Michael Roth ha scritto:
> virtio-blk dataplane currently creates/manages it's own thread to
> offload work to a separate event loop.
>
> This patch insteads allows us to specify a QContext-based event loop by
> adding a "context" property for virtio-blk we can use like so:
>
> qemu ... \
> -object glib-qcontext,id=ctx0,threaded=yes
> -drive file=file.raw,id=drive0,aio=native,cache=none \
> -device virtio-blk,drive=drive0,scsi=off,x-data-plane=on,context=ctx0
>
> virtio-blk dataplane then simply attachs/detaches it's AioContext to the
> ctx0 event loop on start/stop.
>
> This also makes available the option to drive a virtio-blk dataplane via
> the default main loop:
>
> qemu ... \
> -drive file=file.raw,id=drive0,aio=native,cache=none \
> -device virtio-blk,drive=drive0,scsi=off,x-data-plane=on,context=main
>
> This doesn't do much in and of itself, but helps to demonstrate how we
> might model a general mechanism to offload device workloads to separate
> threads.
>
> Signed-off-by: Michael Roth <address@hidden>
> ---
> hw/block/dataplane/virtio-blk.c | 46
> ++++++++++++---------------------------
> include/hw/virtio/virtio-blk.h | 7 ++++--
> 2 files changed, 19 insertions(+), 34 deletions(-)
>
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index 0356665..08ea10f 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -24,6 +24,8 @@
> #include "virtio-blk.h"
> #include "block/aio.h"
> #include "hw/virtio/virtio-bus.h"
> +#include "qcontext/qcontext.h"
> +#include "qcontext/glib-qcontext.h"
>
> enum {
> SEG_MAX = 126, /* maximum number of I/O segments */
> @@ -60,6 +62,7 @@ struct VirtIOBlockDataPlane {
> * use it).
> */
> AioContext *ctx;
> + QContext *qctx;
> EventNotifier io_notifier; /* Linux AIO completion */
> EventNotifier host_notifier; /* doorbell */
>
> @@ -375,26 +378,6 @@ static void handle_io(EventNotifier *e)
> }
> }
>
> -static void *data_plane_thread(void *opaque)
> -{
> - VirtIOBlockDataPlane *s = opaque;
> -
> - do {
> - aio_poll(s->ctx, true);
> - } while (!s->stopping || s->num_reqs > 0);
> - return NULL;
> -}
> -
> -static void start_data_plane_bh(void *opaque)
> -{
> - VirtIOBlockDataPlane *s = opaque;
> -
> - qemu_bh_delete(s->start_bh);
> - s->start_bh = NULL;
> - qemu_thread_create(&s->thread, data_plane_thread,
> - s, QEMU_THREAD_JOINABLE);
> -}
> -
> bool virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *blk,
> VirtIOBlockDataPlane **dataplane)
> {
> @@ -460,6 +443,7 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
> VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
> VirtQueue *vq;
> int i;
> + Error *err = NULL;
>
> if (s->started) {
> return;
> @@ -502,9 +486,16 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
> /* Kick right away to begin processing requests already in vring */
> event_notifier_set(virtio_queue_get_host_notifier(vq));
>
> - /* Spawn thread in BH so it inherits iothread cpusets */
> - s->start_bh = qemu_bh_new(start_data_plane_bh, s);
> - qemu_bh_schedule(s->start_bh);
> + /* use QEMU main loop/context by default */
> + if (!s->blk->context) {
> + s->blk->context = g_strdup("main");
> + }
Or rather create a device-specific context by default?
Paolo
> + s->qctx = qcontext_find_by_name(s->blk->context, &err);
> + if (err) {
> + fprintf(stderr, "virtio-blk failed to start: %s",
> error_get_pretty(err));
> + exit(1);
> + }
> + aio_context_attach(s->ctx, s->qctx);
> }
>
> void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
> @@ -517,15 +508,6 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
> s->stopping = true;
> trace_virtio_blk_data_plane_stop(s);
>
> - /* Stop thread or cancel pending thread creation BH */
> - if (s->start_bh) {
> - qemu_bh_delete(s->start_bh);
> - s->start_bh = NULL;
> - } else {
> - aio_notify(s->ctx);
> - qemu_thread_join(&s->thread);
> - }
> -
> aio_set_event_notifier(s->ctx, &s->io_notifier, NULL, NULL);
> ioq_cleanup(&s->ioqueue);
>
> diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
> index fc71853..c5514a4 100644
> --- a/include/hw/virtio/virtio-blk.h
> +++ b/include/hw/virtio/virtio-blk.h
> @@ -110,6 +110,7 @@ struct VirtIOBlkConf
> uint32_t scsi;
> uint32_t config_wce;
> uint32_t data_plane;
> + char *context;
> };
>
> struct VirtIOBlockDataPlane;
> @@ -138,13 +139,15 @@ typedef struct VirtIOBlock {
> DEFINE_BLOCK_CHS_PROPERTIES(_state, _field.conf),
> \
> DEFINE_PROP_STRING("serial", _state, _field.serial),
> \
> DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true),
> \
> - DEFINE_PROP_BIT("scsi", _state, _field.scsi, 0, true)
> + DEFINE_PROP_BIT("scsi", _state, _field.scsi, 0, true),
> \
> + DEFINE_PROP_STRING("context", _state, _field.context)
> #else
> #define DEFINE_VIRTIO_BLK_PROPERTIES(_state, _field)
> \
> DEFINE_BLOCK_PROPERTIES(_state, _field.conf),
> \
> DEFINE_BLOCK_CHS_PROPERTIES(_state, _field.conf),
> \
> DEFINE_PROP_STRING("serial", _state, _field.serial),
> \
> - DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true)
> + DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true),
> \
> + DEFINE_PROP_STRING("context", _state, _field.context)
> #endif /* __linux__ */
>
> void virtio_blk_set_conf(DeviceState *dev, VirtIOBlkConf *blk);
>
- Re: [Qemu-devel] [PATCH 1/9] qom: add qom_init_completion, (continued)
- [Qemu-devel] [PATCH 3/9] QSource: QEMU event source object, Michael Roth, 2013/05/03
- [Qemu-devel] [PATCH 5/9] GlibQContext: a QContext wrapper around GMainContexts, Michael Roth, 2013/05/03
- [Qemu-devel] [PATCH 4/9] QContext: QEMU event loop context, abstract base class, Michael Roth, 2013/05/03
- [Qemu-devel] [PATCH 6/9] QContext: add unit tests, Michael Roth, 2013/05/03
- [Qemu-devel] [PATCH 8/9] main-loop: drive main event loop via QContext, Michael Roth, 2013/05/03
- [Qemu-devel] [PATCH 7/9] iohandler: associate with main event loop via a QSource, Michael Roth, 2013/05/03
- [Qemu-devel] [PATCH 9/9] dataplane: use a QContext event loop in place of custom thread, Michael Roth, 2013/05/03
- Re: [Qemu-devel] [PATCH 9/9] dataplane: use a QContext event loop in place of custom thread,
Paolo Bonzini <=
- Re: [Qemu-devel] [RFC 0/9] QContext: QOM class to support multiple event loops, liu ping fan, 2013/05/05
- Re: [Qemu-devel] [RFC 0/9] QContext: QOM class to support multiple event loops, Paolo Bonzini, 2013/05/06
- Re: [Qemu-devel] [RFC 0/9] QContext: QOM class to support multiple event loops, mdroth, 2013/05/06