Re: [PATCH v2 3/4] vfio/quirks: ioeventfd quirk acceleration

Peter Xu
2018-05-03T03:36:35Z

On Tue, May 01, 2018 at 10:43:32AM -0600, Alex Williamson wrote:

[...]

> @@ -743,6 +843,60 @@ static void vfio_nvidia_quirk_mirror_write(void *opaque, hwaddr addr,
> addr + mirror->offset, data, size);
> trace_vfio_quirk_nvidia_bar0_msi_ack(vdev->vbasedev.name);
> }
> +
> + /*
> + * Automatically add an ioeventfd to handle any repeated write with the
> + * same data and size above the standard PCI config space header. This is
> + * primarily expected to accelerate the MSI-ACK behavior, such as noted
> + * above. Current hardware/drivers should trigger an ioeventfd at config
> + * offset 0x704 (region offset 0x88704), with data 0x0, size 4.
> + *
> + * The criteria of 10 successive hits is arbitrary but reliably adds the
> + * MSI-ACK region. Note that as some writes are bypassed via the ioeventfd,
> + * the remaining ones have a greater chance of being seen successively.
> + * To avoid the pathological case of burning up all of QEMU's open file
> + * handles, arbitrarily limit this algorithm from adding no more than 10
> + * ioeventfds, print an error if we would have added an 11th, and then
> + * stop counting.
> + */
> + if (!vdev->no_kvm_ioeventfd &&
> + addr > PCI_STD_HEADER_SIZEOF && last->added < MAX_DYN_IOEVENTFD + 1) {
> + if (addr != last->addr || data != last->data || size != last->size) {
> + last->addr = addr;
> + last->data = data;
> + last->size = size;
> + last->hits = 1;
> + } else if (++last->hits >= HITS_FOR_IOEVENTFD) {
> + if (last->added < MAX_DYN_IOEVENTFD) {
> + VFIOIOEventFD *ioeventfd;
> + ioeventfd = vfio_ioeventfd_init(vdev, mirror->mem, addr, size,
> + data, &vdev->bars[mirror->bar].region,
> + mirror->offset + addr, true);
> + if (ioeventfd) {
> + VFIOQuirk *quirk;
> +
> + QLIST_FOREACH(quirk,
> + &vdev->bars[mirror->bar].quirks, next) {

I'm not sure whether the quirks list can be a long one, otherwise not
sure whether we can just cache the quirk pointer inside the mirror to
avoid the loop.

> + if (quirk->data == mirror) {
> + QLIST_INSERT_HEAD(&quirk->ioeventfds,
> + ioeventfd, next);
> + break;
> + }
> + }

[...]

> +typedef struct VFIOIOEventFD {
> + QLIST_ENTRY(VFIOIOEventFD) next;
> + MemoryRegion *mr;
> + hwaddr addr;
> + unsigned size;
> + uint64_t data;
> + EventNotifier e;
> + VFIORegion *region;
> + hwaddr region_addr;
> + bool match_data;

Would it possible in the future that match_data will be false?
Otherwise I'm not sure whether we can even omit this field.

> + bool dynamic;
> +} VFIOIOEventFD;
> +

The two comments are only questions I thought about. No matter what
the patch looks quite good to me already, so:

Reviewed-by: Peter Xu <peterx@redhat.com>

Regards,

--
Peter Xu