Messages in this thread | | | Date | Fri, 08 Sep 2017 19:09:24 +0800 | From | Wei Wang <> | Subject | Re: [virtio-dev] Re: [PATCH v15 3/5] virtio-balloon: VIRTIO_BALLOON_F_SG |
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On 09/08/2017 11:36 AM, Michael S. Tsirkin wrote: > On Tue, Aug 29, 2017 at 11:09:18AM +0800, Wei Wang wrote: >> On 08/29/2017 02:03 AM, Michael S. Tsirkin wrote: >>> On Mon, Aug 28, 2017 at 06:08:31PM +0800, Wei Wang wrote: >>>> Add a new feature, VIRTIO_BALLOON_F_SG, which enables the transfer >>>> of balloon (i.e. inflated/deflated) pages using scatter-gather lists >>>> to the host. >>>> >>>> The implementation of the previous virtio-balloon is not very >>>> efficient, because the balloon pages are transferred to the >>>> host one by one. Here is the breakdown of the time in percentage >>>> spent on each step of the balloon inflating process (inflating >>>> 7GB of an 8GB idle guest). >>>> >>>> 1) allocating pages (6.5%) >>>> 2) sending PFNs to host (68.3%) >>>> 3) address translation (6.1%) >>>> 4) madvise (19%) >>>> >>>> It takes about 4126ms for the inflating process to complete. >>>> The above profiling shows that the bottlenecks are stage 2) >>>> and stage 4). >>>> >>>> This patch optimizes step 2) by transferring pages to the host in >>>> sgs. An sg describes a chunk of guest physically continuous pages. >>>> With this mechanism, step 4) can also be optimized by doing address >>>> translation and madvise() in chunks rather than page by page. >>>> >>>> With this new feature, the above ballooning process takes ~597ms >>>> resulting in an improvement of ~86%. >>>> >>>> TODO: optimize stage 1) by allocating/freeing a chunk of pages >>>> instead of a single page each time. >>>> >>>> Signed-off-by: Wei Wang <wei.w.wang@intel.com> >>>> Signed-off-by: Liang Li <liang.z.li@intel.com> >>>> Suggested-by: Michael S. Tsirkin <mst@redhat.com> >>>> --- >>>> drivers/virtio/virtio_balloon.c | 171 ++++++++++++++++++++++++++++++++---- >>>> include/uapi/linux/virtio_balloon.h | 1 + >>>> 2 files changed, 155 insertions(+), 17 deletions(-) >>>> >>>> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >>>> index f0b3a0b..8ecc1d4 100644 >>>> --- a/drivers/virtio/virtio_balloon.c >>>> +++ b/drivers/virtio/virtio_balloon.c >>>> @@ -32,6 +32,8 @@ >>>> #include <linux/mm.h> >>>> #include <linux/mount.h> >>>> #include <linux/magic.h> >>>> +#include <linux/xbitmap.h> >>>> +#include <asm/page.h> >>>> /* >>>> * Balloon device works in 4K page units. So each page is pointed to by >>>> @@ -79,6 +81,9 @@ struct virtio_balloon { >>>> /* Synchronize access/update to this struct virtio_balloon elements */ >>>> struct mutex balloon_lock; >>>> + /* The xbitmap used to record balloon pages */ >>>> + struct xb page_xb; >>>> + >>>> /* The array of pfns we tell the Host about. */ >>>> unsigned int num_pfns; >>>> __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX]; >>>> @@ -141,13 +146,111 @@ static void set_page_pfns(struct virtio_balloon *vb, >>>> page_to_balloon_pfn(page) + i); >>>> } >>>> +static int add_one_sg(struct virtqueue *vq, void *addr, uint32_t size) >>>> +{ >>>> + struct scatterlist sg; >>>> + >>>> + sg_init_one(&sg, addr, size); >>>> + return virtqueue_add_inbuf(vq, &sg, 1, vq, GFP_KERNEL); >>>> +} >>>> + >>>> +static void send_balloon_page_sg(struct virtio_balloon *vb, >>>> + struct virtqueue *vq, >>>> + void *addr, >>>> + uint32_t size, >>>> + bool batch) >>>> +{ >>>> + unsigned int len; >>>> + int err; >>>> + >>>> + err = add_one_sg(vq, addr, size); >>>> + /* Sanity check: this can't really happen */ >>>> + WARN_ON(err); >>> It might be cleaner to detect that add failed due to >>> ring full and kick then. Just an idea, up to you >>> whether to do it. >>> >>>> + >>>> + /* If batching is in use, we batch the sgs till the vq is full. */ >>>> + if (!batch || !vq->num_free) { >>>> + virtqueue_kick(vq); >>>> + wait_event(vb->acked, virtqueue_get_buf(vq, &len)); >>>> + /* Release all the entries if there are */ >>> Meaning >>> Account for all used entries if any >>> ? >>> >>>> + while (virtqueue_get_buf(vq, &len)) >>>> + ; >>> Above code is reused below. Add a function? >>> >>>> + } >>>> +} >>>> + >>>> +/* >>>> + * Send balloon pages in sgs to host. The balloon pages are recorded in the >>>> + * page xbitmap. Each bit in the bitmap corresponds to a page of PAGE_SIZE. >>>> + * The page xbitmap is searched for continuous "1" bits, which correspond >>>> + * to continuous pages, to chunk into sgs. >>>> + * >>>> + * @page_xb_start and @page_xb_end form the range of bits in the xbitmap that >>>> + * need to be searched. >>>> + */ >>>> +static void tell_host_sgs(struct virtio_balloon *vb, >>>> + struct virtqueue *vq, >>>> + unsigned long page_xb_start, >>>> + unsigned long page_xb_end) >>>> +{ >>>> + unsigned long sg_pfn_start, sg_pfn_end; >>>> + void *sg_addr; >>>> + uint32_t sg_len, sg_max_len = round_down(UINT_MAX, PAGE_SIZE); >>>> + >>>> + sg_pfn_start = page_xb_start; >>>> + while (sg_pfn_start < page_xb_end) { >>>> + sg_pfn_start = xb_find_next_bit(&vb->page_xb, sg_pfn_start, >>>> + page_xb_end, 1); >>>> + if (sg_pfn_start == page_xb_end + 1) >>>> + break; >>>> + sg_pfn_end = xb_find_next_bit(&vb->page_xb, sg_pfn_start + 1, >>>> + page_xb_end, 0); >>>> + sg_addr = (void *)pfn_to_kaddr(sg_pfn_start); >>>> + sg_len = (sg_pfn_end - sg_pfn_start) << PAGE_SHIFT; >>>> + while (sg_len > sg_max_len) { >>>> + send_balloon_page_sg(vb, vq, sg_addr, sg_max_len, 1); >>> Last argument should be true, not 1. >>> >>>> + sg_addr += sg_max_len; >>>> + sg_len -= sg_max_len; >>>> + } >>>> + send_balloon_page_sg(vb, vq, sg_addr, sg_len, 1); >>>> + xb_zero(&vb->page_xb, sg_pfn_start, sg_pfn_end); >>>> + sg_pfn_start = sg_pfn_end + 1; >>>> + } >>>> + >>>> + /* >>>> + * The last few sgs may not reach the batch size, but need a kick to >>>> + * notify the device to handle them. >>>> + */ >>>> + if (vq->num_free != virtqueue_get_vring_size(vq)) { >>>> + virtqueue_kick(vq); >>>> + wait_event(vb->acked, virtqueue_get_buf(vq, &sg_len)); >>>> + while (virtqueue_get_buf(vq, &sg_len)) >>>> + ; >>> Some entries can get used after a pause. Looks like they will leak then? >>> One fix would be to convert above if to a while loop. >>> I don't know whether to do it like this in send_balloon_page_sg too. >>> >> Thanks for the above comments. I've re-written this part of code. >> Please have a check below if there is anything more we could improve: >> >> static void kick_and_wait(struct virtqueue *vq, wait_queue_head_t wq_head) >> { >> unsigned int len; >> >> virtqueue_kick(vq); >> wait_event(wq_head, virtqueue_get_buf(vq, &len)); >> /* Detach all the used buffers from the vq */ >> while (virtqueue_get_buf(vq, &len)) >> ; > I would move this last part to before add_buf. Increases chances > it succeeds even in case of a bug.
> >> } >> >> static int add_one_sg(struct virtqueue *vq, void *addr, uint32_t size) >> { >> struct scatterlist sg; >> int ret; >> >> sg_init_one(&sg, addr, size); >> ret = virtqueue_add_inbuf(vq, &sg, 1, vq, GFP_KERNEL); >> if (unlikely(ret == -ENOSPC)) >> dev_warn(&vq->vdev->dev, "%s: failed due to ring full\n", >> __func__); > So if this ever triggers then kick and wait might fail, right? > I think you should not special-case this one then.
OK, I will remove the check above, and take other suggestions as well. Thanks.
Best, Wei
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