Re: [Xen-devel] [PATCH 3/3] xen-disk: use an IOThread per instance

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Paolo Bonzini [mailto:paolo.bonzini@xxxxxxxxx] On Behalf Of Paolo
> Bonzini
> Sent: 20 June 2017 17:08
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> qemu-devel@xxxxxxxxxx; qemu-block@xxxxxxxxxx
> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>; Kevin Wolf
> <kwolf@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; Max Reitz
> <mreitz@xxxxxxxxxx>
> Subject: Re: [PATCH 3/3] xen-disk: use an IOThread per instance
> 
> On 20/06/2017 15:47, Paul Durrant wrote:
> > This patch allocates an IOThread object for each xen_disk instance and
> > sets the AIO context appropriately on connect. This allows processing
> > of I/O to proceed in parallel.
> >
> > The patch also adds tracepoints into xen_disk to make it possible to
> > follow the state transtions of an instance in the log.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> 
> The QEMU block layer is not yet thread safe, but code running in
> IOThreads still has to take the AioContext lock.  You need to call
> aio_context_acquire/release in blk_bh and qemu_aio_complete.
> 

Ok, thanks. I'll update the patch and re-test.

Cheers,

  Paul

> Paolo
> 
> > ---
> > Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
> > Cc: Kevin Wolf <kwolf@xxxxxxxxxx>
> > Cc: Max Reitz <mreitz@xxxxxxxxxx>
> > ---
> >  hw/block/trace-events |  7 +++++++
> >  hw/block/xen_disk.c   | 44
> +++++++++++++++++++++++++++++++++++++++++++-
> >  2 files changed, 50 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/block/trace-events b/hw/block/trace-events
> > index 65e83dc258..608b24ba66 100644
> > --- a/hw/block/trace-events
> > +++ b/hw/block/trace-events
> > @@ -10,3 +10,10 @@ virtio_blk_submit_multireq(void *mrb, int start, int
> num_reqs, uint64_t offset,
> >  # hw/block/hd-geometry.c
> >  hd_geometry_lchs_guess(void *blk, int cyls, int heads, int secs) "blk %p
> LCHS %d %d %d"
> >  hd_geometry_guess(void *blk, uint32_t cyls, uint32_t heads, uint32_t
> secs, int trans) "blk %p CHS %u %u %u trans %d"
> > +
> > +# hw/block/xen_disk.c
> > +xen_disk_alloc(char *name) "%s"
> > +xen_disk_init(char *name) "%s"
> > +xen_disk_connect(char *name) "%s"
> > +xen_disk_disconnect(char *name) "%s"
> > +xen_disk_free(char *name) "%s"
> > diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
> > index a9942d32db..ec1085c802 100644
> > --- a/hw/block/xen_disk.c
> > +++ b/hw/block/xen_disk.c
> > @@ -27,10 +27,13 @@
> >  #include "hw/xen/xen_backend.h"
> >  #include "xen_blkif.h"
> >  #include "sysemu/blockdev.h"
> > +#include "sysemu/iothread.h"
> >  #include "sysemu/block-backend.h"
> >  #include "qapi/error.h"
> >  #include "qapi/qmp/qdict.h"
> >  #include "qapi/qmp/qstring.h"
> > +#include "qom/object_interfaces.h"
> > +#include "trace.h"
> >
> >  /* ------------------------------------------------------------- */
> >
> > @@ -128,6 +131,9 @@ struct XenBlkDev {
> >      DriveInfo           *dinfo;
> >      BlockBackend        *blk;
> >      QEMUBH              *bh;
> > +
> > +    IOThread            *iothread;
> > +    AioContext          *ctx;
> >  };
> >
> >  /* ------------------------------------------------------------- */
> > @@ -923,11 +929,31 @@ static void blk_bh(void *opaque)
> >  static void blk_alloc(struct XenDevice *xendev)
> >  {
> >      struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev,
> xendev);
> > +    Object *obj;
> > +    char *name;
> > +    Error *err = NULL;
> > +
> > +    trace_xen_disk_alloc(xendev->name);
> >
> >      QLIST_INIT(&blkdev->inflight);
> >      QLIST_INIT(&blkdev->finished);
> >      QLIST_INIT(&blkdev->freelist);
> > -    blkdev->bh = qemu_bh_new(blk_bh, blkdev);
> > +
> > +    obj = object_new(TYPE_IOTHREAD);
> > +    name = g_strdup_printf("iothread-%s", xendev->name);
> > +
> > +    object_property_add_child(object_get_objects_root(), name, obj,
> &err);
> > +    assert(!err);
> > +
> > +    g_free(name);
> > +
> > +    user_creatable_complete(obj, &err);
> > +    assert(!err);
> > +
> > +    blkdev->iothread = (IOThread *)object_dynamic_cast(obj,
> TYPE_IOTHREAD);
> > +    blkdev->ctx = iothread_get_aio_context(blkdev->iothread);
> > +    blkdev->bh = aio_bh_new(blkdev->ctx, blk_bh, blkdev);
> > +
> >      if (xen_mode != XEN_EMULATE) {
> >          batch_maps = 1;
> >      }
> > @@ -954,6 +980,8 @@ static int blk_init(struct XenDevice *xendev)
> >      int info = 0;
> >      char *directiosafe = NULL;
> >
> > +    trace_xen_disk_init(xendev->name);
> > +
> >      /* read xenstore entries */
> >      if (blkdev->params == NULL) {
> >          char *h = NULL;
> > @@ -1069,6 +1097,8 @@ static int blk_connect(struct XenDevice *xendev)
> >      unsigned int i;
> >      uint32_t *domids;
> >
> > +    trace_xen_disk_connect(xendev->name);
> > +
> >      /* read-only ? */
> >      if (blkdev->directiosafe) {
> >          qflags = BDRV_O_NOCACHE | BDRV_O_NATIVE_AIO;
> > @@ -1285,6 +1315,8 @@ static int blk_connect(struct XenDevice *xendev)
> >          blkdev->persistent_gnt_count = 0;
> >      }
> >
> > +    blk_set_aio_context(blkdev->blk, blkdev->ctx);
> > +
> >      xen_be_bind_evtchn(&blkdev->xendev);
> >
> >      xen_pv_printf(&blkdev->xendev, 1, "ok: proto %s, nr-ring-ref %u, "
> > @@ -1298,13 +1330,20 @@ static void blk_disconnect(struct XenDevice
> *xendev)
> >  {
> >      struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev,
> xendev);
> >
> > +    trace_xen_disk_disconnect(xendev->name);
> > +
> > +    aio_context_acquire(blkdev->ctx);
> > +
> >      if (blkdev->blk) {
> > +        blk_set_aio_context(blkdev->blk, qemu_get_aio_context());
> >          blk_detach_dev(blkdev->blk, blkdev);
> >          blk_unref(blkdev->blk);
> >          blkdev->blk = NULL;
> >      }
> >      xen_pv_unbind_evtchn(&blkdev->xendev);
> >
> > +    aio_context_release(blkdev->ctx);
> > +
> >      if (blkdev->sring) {
> >          xengnttab_unmap(blkdev->xendev.gnttabdev, blkdev->sring,
> >                          blkdev->nr_ring_ref);
> > @@ -1338,6 +1377,8 @@ static int blk_free(struct XenDevice *xendev)
> >      struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev,
> xendev);
> >      struct ioreq *ioreq;
> >
> > +    trace_xen_disk_free(xendev->name);
> > +
> >      if (blkdev->blk || blkdev->sring) {
> >          blk_disconnect(xendev);
> >      }
> > @@ -1355,6 +1396,7 @@ static int blk_free(struct XenDevice *xendev)
> >      g_free(blkdev->dev);
> >      g_free(blkdev->devtype);
> >      qemu_bh_delete(blkdev->bh);
> > +    object_unparent(OBJECT(blkdev->iothread));
> >      return 0;
> >  }
> >
> >
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