On Thu, Nov 12, 2020 at 05:18:59PM -0600, Mike Christie wrote: > The following kernel patches were made over Michael's vhost branch: > > https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/log/?h=vhost > > and the vhost-scsi bug fix patchset: > > https://lore.kernel.org/linux-scsi/[email protected]/T/#t > > And the qemu patch was made over the qemu master branch. > > vhost-scsi currently supports multiple queues with the num_queues > setting, but we end up with a setup where the guest's scsi/block > layer can do a queue per vCPU and the layers below vhost can do > a queue per CPU. vhost-scsi will then do a num_queue virtqueues, > but all IO gets set on and completed on a single vhost-scsi thread. > After 2 - 4 vqs this becomes a bottleneck. > > This patchset allows us to create a worker thread per IO vq, so we > can better utilize multiple CPUs with the multiple queues. It > implments Jason's suggestion to create the initial worker like > normal, then create the extra workers for IO vqs with the > VHOST_SET_VRING_ENABLE ioctl command added in this patchset.
How does userspace find out the tids and set their CPU affinity?
What is the meaning of the new VHOST_SET_VRING_ENABLE ioctl? It doesn't
really "enable" or "disable" the vq, requests are processed regardless.
The purpose of the ioctl isn't clear to me because the kernel could
automatically create 1 thread per vq without a new ioctl. On the other
hand, if userspace is supposed to control worker threads then a
different interface would be more powerful:
struct vhost_vq_worker_info {
/*
* The pid of an existing vhost worker that this vq will be
* assigned to. When pid is 0 the virtqueue is assigned to the
* default vhost worker. When pid is -1 a new worker thread is
* created for this virtqueue. When pid is -2 the virtqueue's
* worker thread is unchanged.
*
* If a vhost worker no longer has any virtqueues assigned to it
* then it will terminate.
*
* The pid of the vhost worker is stored to this field when the
* ioctl completes successfully. Use pid -2 to query the current
* vhost worker pid.
*/
__kernel_pid_t pid; /* in/out */
/* The virtqueue index*/
unsigned int vq_idx; /* in */
};
ioctl(vhost_fd, VHOST_SET_VQ_WORKER, &info);
Stefan
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