On 2015/4/3 0:26, Fam Zheng wrote:
> On Thu, 04/02 17:21, Paolo Bonzini wrote:
>>
>>
>> On 02/04/2015 17:16, Fam Zheng wrote:
>>>>>>>>> After qemu_iovec_destroy, the QEMUIOVector's size is zeroed and
>>>>>>>>> the zero size ultimately is used to compute virtqueue_push's len
>>>>>>>>> argument. Therefore, reads from virtio-blk devices did not
>>>>>>>>> migrate their results correctly. (Writes were okay).
>>>>>>>
>>>>>>> Can't we move qemu_iovec_destroy to virtio_blk_free_request?
>>>>>
>>>>> You would still have to add more code to differentiate reads and
>>>>> writes---I think.
>>> Yeah, but the extra field will not be needed.
>>
>> Can you post an alternative patch? One small complication is that
>> is_write is in mrb but not in mrb->reqs[x]. virtio_blk_rw_complete is
>> already doing
>>
>> int p = virtio_ldl_p(VIRTIO_DEVICE(req->dev), &req->out.type);
>> bool is_read = !(p & VIRTIO_BLK_T_OUT);
>>
>> but only in a slow path.
>
> OK, so it looks like a new field is the simplest way to achieve.
>
> There is another problem with your patch - read_size is not initialized in
> non-RW paths like scsi and flush.
>
> I think the optimization for write is a separate thing, though. Shouldn't
> below
> patch already fix the migration issue?
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 000c38d..ee6e198 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -92,13 +92,6 @@ static void virtio_blk_rw_complete(void *opaque, int ret)
> next = req->mr_next;
> trace_virtio_blk_rw_complete(req, ret);
>
> - if (req->qiov.nalloc != -1) {
> - /* If nalloc is != 1 req->qiov is a local copy of the original
> - * external iovec. It was allocated in submit_merged_requests
> - * to be able to merge requests. */
> - qemu_iovec_destroy(&req->qiov);
> - }
> -
> if (ret) {
> int p = virtio_ldl_p(VIRTIO_DEVICE(req->dev), &req->out.type);
> bool is_read = !(p & VIRTIO_BLK_T_OUT);
> @@ -109,6 +102,13 @@ static void virtio_blk_rw_complete(void *opaque, int ret)
>
> virtio_blk_req_complete(req, VIRTIO_BLK_S_OK);
> block_acct_done(blk_get_stats(req->dev->blk), &req->acct);
> +
> + if (req->qiov.nalloc != -1) {
> + /* This means req->qiov is a local copy of the original external
> + * iovec. It was allocated in virtio_blk_submit_multireq in order
> + * to merge requests. */
> + qemu_iovec_destroy(&req->qiov);
> + }
> virtio_blk_free_request(req);
> }
> }
>
>
>
> .
>
Can we allocate a new request for the merged requests?
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 000c38d..d39381f 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -92,11 +92,10 @@ static void virtio_blk_rw_complete(void *opaque, int ret)
next = req->mr_next;
trace_virtio_blk_rw_complete(req, ret);
- if (req->qiov.nalloc != -1) {
- /* If nalloc is != 1 req->qiov is a local copy of the original
- * external iovec. It was allocated in submit_merged_requests
- * to be able to merge requests. */
+ if (req->in == NULL) {
qemu_iovec_destroy(&req->qiov);
+ virtio_blk_free_request(req);
+ continue;
}
if (ret) {
@@ -313,29 +312,33 @@ static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
static inline void submit_requests(BlockBackend *blk, MultiReqBuffer *mrb,
int start, int num_reqs, int niov)
{
- QEMUIOVector *qiov = &mrb->reqs[start]->qiov;
+ VirtIOBlockReq *merged_request;
+ QEMUIOVector *qiov;
int64_t sector_num = mrb->reqs[start]->sector_num;
- int nb_sectors = mrb->reqs[start]->qiov.size / BDRV_SECTOR_SIZE;
+ int nb_sectors = 0;
bool is_write = mrb->is_write;
if (num_reqs > 1) {
int i;
- struct iovec *tmp_iov = qiov->iov;
- int tmp_niov = qiov->niov;
- /* mrb->reqs[start]->qiov was initialized from external so we can't
- * modifiy it here. We need to initialize it locally and then add the
- * external iovecs. */
- qemu_iovec_init(qiov, niov)
+ merged_request = virtio_blk_alloc_request(mrb->reqs[start]->dev);
- for (i = 0; i < tmp_niov; i++) {
- qemu_iovec_add(qiov, tmp_iov[i].iov_base, tmp_iov[i].iov_len);
- }
+ /* use the 'in' field to judge whether the request is
+ a merged request */
+ merged_request->in = NULL;
+
+ qiov = &merged_request->qiov;
+ qemu_iovec_init(qiov, niov);
- for (i = start + 1; i < start + num_reqs; i++) {
+ for (i = start; i < start + num_reqs; i++) {
qemu_iovec_concat(qiov, &mrb->reqs[i]->qiov, 0,
mrb->reqs[i]->qiov.size);
- mrb->reqs[i - 1]->mr_next = mrb->reqs[i];
+ if (i > start) {
+ mrb->reqs[i - 1]->mr_next = mrb->reqs[i];
+ } else {
+ merged_request->mr_next = mrb->reqs[i];
+ }
+
nb_sectors += mrb->reqs[i]->qiov.size / BDRV_SECTOR_SIZE;
}
assert(nb_sectors == qiov->size / BDRV_SECTOR_SIZE);
@@ -345,14 +348,18 @@ static inline void submit_requests(BlockBackend *blk,
MultiReqBuffer *mrb,
block_acct_merge_done(blk_get_stats(blk),
is_write ? BLOCK_ACCT_WRITE : BLOCK_ACCT_READ,
num_reqs - 1);
+ } else {
+ merged_request = mrb->reqs[start];
+ qiov = &mrb->reqs[start]->qiov;
+ nb_sectors = mrb->reqs[start]->qiov.size / BDRV_SECTOR_SIZE;
}
if (is_write) {
blk_aio_writev(blk, sector_num, qiov, nb_sectors,
- virtio_blk_rw_complete, mrb->reqs[start]);
+ virtio_blk_rw_complete, merged_request);
} else {
blk_aio_readv(blk, sector_num, qiov, nb_sectors,
- virtio_blk_rw_complete, mrb->reqs[start]);
+ virtio_blk_rw_complete, merged_request);
}
}
--
Bin Wu
