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xen_disk: use a single entry iovec 

Since xen_disk now always copies data to and from a guest there is no need
to maintain a vector entry corresponding to every page of a request.
This means there is less per-request state to maintain so the ioreq
structure can shrink significantly.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
This commit is contained in:
Paul Durrant 2018-05-17 16:35:57 +01:00 committed by Stefano Stabellini
parent a68bf540f6
commit 5ebf962652
1 changed files with 21 additions and 55 deletions
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76
hw/block/xen_disk.c
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@ -46,13 +46,10 @@ struct ioreq {
/* parsed request */
off_t start;
QEMUIOVector v;
void *buf;
size_t size;
int presync;
/* grant mapping */
uint32_t refs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
void *page[BLKIF_MAX_SEGMENTS_PER_REQUEST];
void *pages;
/* aio status */
int aio_inflight;
int aio_errors;
@ -110,12 +107,10 @@ static void ioreq_reset(struct ioreq *ioreq)
memset(&ioreq->req, 0, sizeof(ioreq->req));
ioreq->status = 0;
ioreq->start = 0;
ioreq->buf = NULL;
ioreq->size = 0;
ioreq->presync = 0;
memset(ioreq->refs, 0, sizeof(ioreq->refs));
memset(ioreq->page, 0, sizeof(ioreq->page));
ioreq->pages = NULL;
ioreq->aio_inflight = 0;
ioreq->aio_errors = 0;
@ -138,7 +133,7 @@ static struct ioreq *ioreq_start(struct XenBlkDev *blkdev)
ioreq = g_malloc0(sizeof(*ioreq));
ioreq->blkdev = blkdev;
blkdev->requests_total++;
qemu_iovec_init(&ioreq->v, BLKIF_MAX_SEGMENTS_PER_REQUEST);
qemu_iovec_init(&ioreq->v, 1);
} else {
/* get one from freelist */
ioreq = QLIST_FIRST(&blkdev->freelist);
@ -183,7 +178,6 @@ static void ioreq_release(struct ioreq *ioreq, bool finish)
static int ioreq_parse(struct ioreq *ioreq)
{
struct XenBlkDev *blkdev = ioreq->blkdev;
uintptr_t mem;
size_t len;
int i;
@ -230,13 +224,10 @@ static int ioreq_parse(struct ioreq *ioreq)
goto err;
}
ioreq->refs[i] = ioreq->req.seg[i].gref;
mem = ioreq->req.seg[i].first_sect * blkdev->file_blk;
len = (ioreq->req.seg[i].last_sect - ioreq->req.seg[i].first_sect + 1) * blkdev->file_blk;
qemu_iovec_add(&ioreq->v, (void*)mem, len);
ioreq->size += len;
}
if (ioreq->start + ioreq->v.size > blkdev->file_size) {
if (ioreq->start + ioreq->size > blkdev->file_size) {
xen_pv_printf(&blkdev->xendev, 0, "error: access beyond end of file\n");
goto err;
}
@ -247,35 +238,6 @@ err:
return -1;
}
static void ioreq_free_copy_buffers(struct ioreq *ioreq)
{
int i;
for (i = 0; i < ioreq->v.niov; i++) {
ioreq->page[i] = NULL;
}
qemu_vfree(ioreq->pages);
}
static int ioreq_init_copy_buffers(struct ioreq *ioreq)
{
int i;
if (ioreq->v.niov == 0) {
return 0;
}
ioreq->pages = qemu_memalign(XC_PAGE_SIZE, ioreq->v.niov * XC_PAGE_SIZE);
for (i = 0; i < ioreq->v.niov; i++) {
ioreq->page[i] = ioreq->pages + i * XC_PAGE_SIZE;
ioreq->v.iov[i].iov_base = ioreq->page[i];
}
return 0;
}
static int ioreq_grant_copy(struct ioreq *ioreq)
{
struct XenBlkDev *blkdev = ioreq->blkdev;
@ -284,25 +246,27 @@ static int ioreq_grant_copy(struct ioreq *ioreq)
int i, count, rc;
int64_t file_blk = ioreq->blkdev->file_blk;
bool to_domain = (ioreq->req.operation == BLKIF_OP_READ);
void *virt = ioreq->buf;
if (ioreq->v.niov == 0) {
if (ioreq->req.nr_segments == 0) {
return 0;
}
count = ioreq->v.niov;
count = ioreq->req.nr_segments;
for (i = 0; i < count; i++) {
if (to_domain) {
segs[i].dest.foreign.ref = ioreq->refs[i];
segs[i].dest.foreign.ref = ioreq->req.seg[i].gref;
segs[i].dest.foreign.offset = ioreq->req.seg[i].first_sect * file_blk;
segs[i].source.virt = ioreq->v.iov[i].iov_base;
segs[i].source.virt = virt;
} else {
segs[i].source.foreign.ref = ioreq->refs[i];
segs[i].source.foreign.ref = ioreq->req.seg[i].gref;
segs[i].source.foreign.offset = ioreq->req.seg[i].first_sect * file_blk;
segs[i].dest.virt = ioreq->v.iov[i].iov_base;
segs[i].dest.virt = virt;
}
segs[i].len = (ioreq->req.seg[i].last_sect
- ioreq->req.seg[i].first_sect + 1) * file_blk;
virt += segs[i].len;
}
rc = xen_be_copy_grant_refs(xendev, to_domain, segs, count);
@ -348,14 +312,14 @@ static void qemu_aio_complete(void *opaque, int ret)
if (ret == 0) {
ioreq_grant_copy(ioreq);
}
ioreq_free_copy_buffers(ioreq);
qemu_vfree(ioreq->buf);
break;
case BLKIF_OP_WRITE:
case BLKIF_OP_FLUSH_DISKCACHE:
if (!ioreq->req.nr_segments) {
break;
}
ioreq_free_copy_buffers(ioreq);
qemu_vfree(ioreq->buf);
break;
default:
break;
@ -423,12 +387,12 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
{
struct XenBlkDev *blkdev = ioreq->blkdev;
ioreq_init_copy_buffers(ioreq);
ioreq->buf = qemu_memalign(XC_PAGE_SIZE, ioreq->size);
if (ioreq->req.nr_segments &&
(ioreq->req.operation == BLKIF_OP_WRITE ||
ioreq->req.operation == BLKIF_OP_FLUSH_DISKCACHE) &&
ioreq_grant_copy(ioreq)) {
ioreq_free_copy_buffers(ioreq);
qemu_vfree(ioreq->buf);
goto err;
}
@ -440,6 +404,7 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
switch (ioreq->req.operation) {
case BLKIF_OP_READ:
qemu_iovec_add(&ioreq->v, ioreq->buf, ioreq->size);
block_acct_start(blk_get_stats(blkdev->blk), &ioreq->acct,
ioreq->v.size, BLOCK_ACCT_READ);
ioreq->aio_inflight++;
@ -452,6 +417,7 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
break;
}
qemu_iovec_add(&ioreq->v, ioreq->buf, ioreq->size);
block_acct_start(blk_get_stats(blkdev->blk), &ioreq->acct,
ioreq->v.size,
ioreq->req.operation == BLKIF_OP_WRITE ?