From d550dda192c1bd039afb774b99485e88b70d7cb8 Mon Sep 17 00:00:00 2001 From: Nadav Har'El Date: Mon, 27 Feb 2012 15:07:29 +0200 Subject: vhost: don't forget to schedule() This is a tiny, but important, patch to vhost. Vhost's worker thread only called schedule() when it had no work to do, and it wanted to go to sleep. But if there's always work to do, e.g., the guest is running a network-intensive program like netperf with small message sizes, schedule() was *never* called. This had several negative implications (on non-preemptive kernels): 1. Passing time was not properly accounted to the "vhost" process (ps and top would wrongly show it using zero CPU time). 2. Sometimes error messages about RCU timeouts would be printed, if the core running the vhost thread didn't schedule() for a very long time. 3. Worst of all, a vhost thread would "hog" the core. If several vhost threads need to share the same core, typically one would get most of the CPU time (and its associated guest most of the performance), while the others hardly get any work done. The trivial solution is to add if (need_resched()) schedule(); After doing every piece of work. This will not do the heavy schedule() all the time, just when the timer interrupt decided a reschedule is warranted (so need_resched returns true). Thanks to Abel Gordon for this patch. Signed-off-by: Nadav Har'El Signed-off-by: Michael S. Tsirkin --- drivers/vhost/vhost.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'drivers/vhost') diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index c14c42b95ab8..ae66278e4dcf 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -222,6 +222,8 @@ static int vhost_worker(void *data) if (work) { __set_current_state(TASK_RUNNING); work->fn(work); + if (need_resched()) + schedule(); } else schedule(); -- cgit v1.2.3 From ea5d404655ba3b356d0c06d6a3c4f24112124522 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Sun, 27 Nov 2011 19:05:58 +0200 Subject: vhost: fix release path lockdep checks We shouldn't hold any locks on release path. Pass a flag to vhost_dev_cleanup to use the lockdep info correctly. Signed-off-by: Michael S. Tsirkin Tested-by: Sasha Levin --- drivers/vhost/net.c | 2 +- drivers/vhost/vhost.c | 9 +++++---- drivers/vhost/vhost.h | 2 +- 3 files changed, 7 insertions(+), 6 deletions(-) (limited to 'drivers/vhost') diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 9dab1f51dd43..f0da2c32fbde 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -588,7 +588,7 @@ static int vhost_net_release(struct inode *inode, struct file *f) vhost_net_stop(n, &tx_sock, &rx_sock); vhost_net_flush(n); - vhost_dev_cleanup(&n->dev); + vhost_dev_cleanup(&n->dev, false); if (tx_sock) fput(tx_sock->file); if (rx_sock) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index ae66278e4dcf..385d8ee0d2d1 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -405,7 +405,7 @@ long vhost_dev_reset_owner(struct vhost_dev *dev) if (!memory) return -ENOMEM; - vhost_dev_cleanup(dev); + vhost_dev_cleanup(dev, true); memory->nregions = 0; RCU_INIT_POINTER(dev->memory, memory); @@ -436,8 +436,8 @@ int vhost_zerocopy_signal_used(struct vhost_virtqueue *vq) return j; } -/* Caller should have device mutex */ -void vhost_dev_cleanup(struct vhost_dev *dev) +/* Caller should have device mutex if and only if locked is set */ +void vhost_dev_cleanup(struct vhost_dev *dev, bool locked) { int i; @@ -474,7 +474,8 @@ void vhost_dev_cleanup(struct vhost_dev *dev) dev->log_file = NULL; /* No one will access memory at this point */ kfree(rcu_dereference_protected(dev->memory, - lockdep_is_held(&dev->mutex))); + locked == + lockdep_is_held(&dev->mutex))); RCU_INIT_POINTER(dev->memory, NULL); WARN_ON(!list_empty(&dev->work_list)); if (dev->worker) { diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h index a801e2821d03..8dcf4cca6bf2 100644 --- a/drivers/vhost/vhost.h +++ b/drivers/vhost/vhost.h @@ -163,7 +163,7 @@ struct vhost_dev { long vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue *vqs, int nvqs); long vhost_dev_check_owner(struct vhost_dev *); long vhost_dev_reset_owner(struct vhost_dev *); -void vhost_dev_cleanup(struct vhost_dev *); +void vhost_dev_cleanup(struct vhost_dev *, bool locked); long vhost_dev_ioctl(struct vhost_dev *, unsigned int ioctl, unsigned long arg); int vhost_vq_access_ok(struct vhost_virtqueue *vq); int vhost_log_access_ok(struct vhost_dev *); -- cgit v1.2.3