RE: [PATCH RFC server 05/11] vfio-user: run vfio-user context

[Thanos Makatos <thanos.makatos@nutanix.com>]

> -----Original Message-----
> From: Jagannathan Raman <jag.raman@oracle.com>
> Sent: 19 July 2021 21:00
> To: qemu-devel@nongnu.org
> Cc: stefanha@redhat.com; alex.williamson@redhat.com;
> elena.ufimtseva@oracle.com; John Levon <john.levon@nutanix.com>;
> john.g.johnson@oracle.com; Thanos Makatos
> <thanos.makatos@nutanix.com>; Swapnil Ingle
> <swapnil.ingle@nutanix.com>; jag.raman@oracle.com
> Subject: [PATCH RFC server 05/11] vfio-user: run vfio-user context
> 
> Setup a separate thread to run the vfio-user context. The thread acts as
> the main loop for the device.

In your "vfio-user: instantiate vfio-user context" patch you create the vfu context in blocking-mode, so the only way to run device emulation is in a separate thread.
Were you going to create a separate thread anyway? You can run device emulation in polling mode therefore you can avoid creating a separate thread, thus saving resources. Do plan to do that in the future?

> 
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> ---
>  hw/remote/vfio-user-obj.c | 44
> ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
> 
> diff --git a/hw/remote/vfio-user-obj.c b/hw/remote/vfio-user-obj.c
> index e362709..6a2d0f5 100644
> --- a/hw/remote/vfio-user-obj.c
> +++ b/hw/remote/vfio-user-obj.c
> @@ -35,6 +35,7 @@
>  #include "trace.h"
>  #include "sysemu/runstate.h"
>  #include "qemu/notify.h"
> +#include "qemu/thread.h"
>  #include "qapi/error.h"
>  #include "sysemu/sysemu.h"
>  #include "hw/qdev-core.h"
> @@ -66,6 +67,8 @@ struct VfuObject {
>      vfu_ctx_t *vfu_ctx;
> 
>      PCIDevice *pci_dev;
> +
> +    QemuThread vfu_ctx_thread;
>  };
> 
>  static void vfu_object_set_socket(Object *obj, const char *str, Error **errp)
> @@ -90,6 +93,44 @@ static void vfu_object_set_devid(Object *obj, const
> char *str, Error **errp)
>      trace_vfu_prop("devid", str);
>  }
> 
> +static void *vfu_object_ctx_run(void *opaque)
> +{
> +    VfuObject *o = opaque;
> +    int ret;
> +
> +    ret = vfu_realize_ctx(o->vfu_ctx);
> +    if (ret < 0) {
> +        error_setg(&error_abort, "vfu: Failed to realize device %s- %s",
> +                   o->devid, strerror(errno));
> +        return NULL;
> +    }
> +
> +    ret = vfu_attach_ctx(o->vfu_ctx);
> +    if (ret < 0) {
> +        error_setg(&error_abort,
> +                   "vfu: Failed to attach device %s to context - %s",
> +                   o->devid, strerror(errno));
> +        return NULL;
> +    }
> +
> +    do {
> +        ret = vfu_run_ctx(o->vfu_ctx);
> +        if (ret < 0) {
> +            if (errno == EINTR) {
> +                ret = 0;
> +            } else if (errno == ENOTCONN) {
> +                object_unparent(OBJECT(o));
> +                break;
> +            } else {
> +                error_setg(&error_abort, "vfu: Failed to run device %s - %s",
> +                           o->devid, strerror(errno));
> +            }
> +        }
> +    } while (ret == 0);
> +
> +    return NULL;
> +}
> +
>  static void vfu_object_machine_done(Notifier *notifier, void *data)
>  {
>      VfuObject *o = container_of(notifier, VfuObject, machine_done);
> @@ -125,6 +166,9 @@ static void vfu_object_machine_done(Notifier
> *notifier, void *data)
>                     pci_get_word(o->pci_dev->config + PCI_DEVICE_ID),
>                     pci_get_word(o->pci_dev->config +
> PCI_SUBSYSTEM_VENDOR_ID),
>                     pci_get_word(o->pci_dev->config + PCI_SUBSYSTEM_ID));
> +
> +    qemu_thread_create(&o->vfu_ctx_thread, "VFU ctx runner",
> vfu_object_ctx_run,
> +                       o, QEMU_THREAD_JOINABLE);
>  }
> 
>  static void vfu_object_init(Object *obj)
> --
> 1.8.3.1