| Message ID | 1363920748-32139-2-git-send-email-asias@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Mar 22, 2013 at 10:52:27AM +0800, Asias He wrote: > Currently, vs->vs_endpoint is used indicate if the endpoint is setup or > not. It is set or cleared in vhost_scsi_set_endpoint() or > vhost_scsi_clear_endpoint() under the vs->dev.mutex lock. However, when > we check it in vhost_scsi_handle_vq(), we ignored the lock. > > Instead of using the vs->vs_endpoint and the vs->dev.mutex lock to > indicate the status of the endpoint, we use per virtqueue > vq->private_data to indicate it. In this way, we can only take the > vq->mutex lock which is per queue and make the concurrent multiqueue > process having less lock contention. Further, in the read side of > vq->private_data, we can even do not take only lock if it is accessed in > the vhost worker thread, because it is protected by "vhost rcu". > > Signed-off-by: Asias He <asias@redhat.com> Need to think some more about this, in any case, not 3.9 material IMO. > --- > drivers/vhost/tcm_vhost.c | 46 ++++++++++++++++++++++++++++++++++++++++------ > 1 file changed, 40 insertions(+), 6 deletions(-) > > diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c > index 43fb11e..099feef 100644 > --- a/drivers/vhost/tcm_vhost.c > +++ b/drivers/vhost/tcm_vhost.c > @@ -67,7 +67,6 @@ struct vhost_scsi { > /* Protected by vhost_scsi->dev.mutex */ > struct tcm_vhost_tpg *vs_tpg[VHOST_SCSI_MAX_TARGET]; > char vs_vhost_wwpn[TRANSPORT_IQN_LEN]; > - bool vs_endpoint; > > struct vhost_dev dev; > struct vhost_virtqueue vqs[VHOST_SCSI_MAX_VQ]; > @@ -91,6 +90,24 @@ static int iov_num_pages(struct iovec *iov) > ((unsigned long)iov->iov_base & PAGE_MASK)) >> PAGE_SHIFT; > } > > +static bool tcm_vhost_check_endpoint(struct vhost_virtqueue *vq) > +{ > + bool ret = false; > + > + /* > + * We can handle the vq only after the endpoint is setup by calling the > + * VHOST_SCSI_SET_ENDPOINT ioctl. > + * > + * TODO: Check that we are running from vhost_worker which acts > + * as read-side critical section for vhost kind of RCU. > + * See the comments in struct vhost_virtqueue in drivers/vhost/vhost.h > + */ > + if (rcu_dereference_check(vq->private_data, 1)) > + ret = true; > + > + return ret; > +} > + > static int tcm_vhost_check_true(struct se_portal_group *se_tpg) > { > return 1; > @@ -581,8 +598,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs, > int head, ret; > u8 target; > > - /* Must use ioctl VHOST_SCSI_SET_ENDPOINT */ > - if (unlikely(!vs->vs_endpoint)) > + if (!tcm_vhost_check_endpoint(vq)) > return; > > mutex_lock(&vq->mutex); > @@ -781,8 +797,9 @@ static int vhost_scsi_set_endpoint( > { > struct tcm_vhost_tport *tv_tport; > struct tcm_vhost_tpg *tv_tpg; > + struct vhost_virtqueue *vq; > bool match = false; > - int index, ret; > + int index, ret, i; > > mutex_lock(&vs->dev.mutex); > /* Verify that ring has been setup correctly. */ > @@ -826,7 +843,13 @@ static int vhost_scsi_set_endpoint( > if (match) { > memcpy(vs->vs_vhost_wwpn, t->vhost_wwpn, > sizeof(vs->vs_vhost_wwpn)); > - vs->vs_endpoint = true; > + for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) { > + vq = &vs->vqs[i]; > + /* Flushing the vhost_work acts as synchronize_rcu */ > + mutex_lock(&vq->mutex); > + rcu_assign_pointer(vq->private_data, vs); > + mutex_unlock(&vq->mutex); > + } > ret = 0; > } else { > ret = -EEXIST; > @@ -842,6 +865,8 @@ static int vhost_scsi_clear_endpoint( > { > struct tcm_vhost_tport *tv_tport; > struct tcm_vhost_tpg *tv_tpg; > + struct vhost_virtqueue *vq; > + bool match = false; > int index, ret, i; > u8 target; > > @@ -877,9 +902,18 @@ static int vhost_scsi_clear_endpoint( > } > tv_tpg->tv_tpg_vhost_count--; > vs->vs_tpg[target] = NULL; > - vs->vs_endpoint = false; > + match = true; > mutex_unlock(&tv_tpg->tv_tpg_mutex); > } > + if (match) { > + for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) { > + vq = &vs->vqs[i]; > + /* Flushing the vhost_work acts as synchronize_rcu */ > + mutex_lock(&vq->mutex); > + rcu_assign_pointer(vq->private_data, NULL); > + mutex_unlock(&vq->mutex); > + } > + } > mutex_unlock(&vs->dev.mutex); > return 0; > > -- > 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c index 43fb11e..099feef 100644 --- a/drivers/vhost/tcm_vhost.c +++ b/drivers/vhost/tcm_vhost.c @@ -67,7 +67,6 @@ struct vhost_scsi { /* Protected by vhost_scsi->dev.mutex */ struct tcm_vhost_tpg *vs_tpg[VHOST_SCSI_MAX_TARGET]; char vs_vhost_wwpn[TRANSPORT_IQN_LEN]; - bool vs_endpoint; struct vhost_dev dev; struct vhost_virtqueue vqs[VHOST_SCSI_MAX_VQ]; @@ -91,6 +90,24 @@ static int iov_num_pages(struct iovec *iov) ((unsigned long)iov->iov_base & PAGE_MASK)) >> PAGE_SHIFT; } +static bool tcm_vhost_check_endpoint(struct vhost_virtqueue *vq) +{ + bool ret = false; + + /* + * We can handle the vq only after the endpoint is setup by calling the + * VHOST_SCSI_SET_ENDPOINT ioctl. + * + * TODO: Check that we are running from vhost_worker which acts + * as read-side critical section for vhost kind of RCU. + * See the comments in struct vhost_virtqueue in drivers/vhost/vhost.h + */ + if (rcu_dereference_check(vq->private_data, 1)) + ret = true; + + return ret; +} + static int tcm_vhost_check_true(struct se_portal_group *se_tpg) { return 1; @@ -581,8 +598,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs, int head, ret; u8 target; - /* Must use ioctl VHOST_SCSI_SET_ENDPOINT */ - if (unlikely(!vs->vs_endpoint)) + if (!tcm_vhost_check_endpoint(vq)) return; mutex_lock(&vq->mutex); @@ -781,8 +797,9 @@ static int vhost_scsi_set_endpoint( { struct tcm_vhost_tport *tv_tport; struct tcm_vhost_tpg *tv_tpg; + struct vhost_virtqueue *vq; bool match = false; - int index, ret; + int index, ret, i; mutex_lock(&vs->dev.mutex); /* Verify that ring has been setup correctly. */ @@ -826,7 +843,13 @@ static int vhost_scsi_set_endpoint( if (match) { memcpy(vs->vs_vhost_wwpn, t->vhost_wwpn, sizeof(vs->vs_vhost_wwpn)); - vs->vs_endpoint = true; + for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) { + vq = &vs->vqs[i]; + /* Flushing the vhost_work acts as synchronize_rcu */ + mutex_lock(&vq->mutex); + rcu_assign_pointer(vq->private_data, vs); + mutex_unlock(&vq->mutex); + } ret = 0; } else { ret = -EEXIST; @@ -842,6 +865,8 @@ static int vhost_scsi_clear_endpoint( { struct tcm_vhost_tport *tv_tport; struct tcm_vhost_tpg *tv_tpg; + struct vhost_virtqueue *vq; + bool match = false; int index, ret, i; u8 target; @@ -877,9 +902,18 @@ static int vhost_scsi_clear_endpoint( } tv_tpg->tv_tpg_vhost_count--; vs->vs_tpg[target] = NULL; - vs->vs_endpoint = false; + match = true; mutex_unlock(&tv_tpg->tv_tpg_mutex); } + if (match) { + for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) { + vq = &vs->vqs[i]; + /* Flushing the vhost_work acts as synchronize_rcu */ + mutex_lock(&vq->mutex); + rcu_assign_pointer(vq->private_data, NULL); + mutex_unlock(&vq->mutex); + } + } mutex_unlock(&vs->dev.mutex); return 0;
Currently, vs->vs_endpoint is used indicate if the endpoint is setup or not. It is set or cleared in vhost_scsi_set_endpoint() or vhost_scsi_clear_endpoint() under the vs->dev.mutex lock. However, when we check it in vhost_scsi_handle_vq(), we ignored the lock. Instead of using the vs->vs_endpoint and the vs->dev.mutex lock to indicate the status of the endpoint, we use per virtqueue vq->private_data to indicate it. In this way, we can only take the vq->mutex lock which is per queue and make the concurrent multiqueue process having less lock contention. Further, in the read side of vq->private_data, we can even do not take only lock if it is accessed in the vhost worker thread, because it is protected by "vhost rcu". Signed-off-by: Asias He <asias@redhat.com> --- drivers/vhost/tcm_vhost.c | 46 ++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 40 insertions(+), 6 deletions(-)