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xen-block: implement indirect descriptors
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Indirect descriptors introduce a new block operation
(BLKIF_OP_INDIRECT) that passes grant references instead of segments
in the request. This grant references are filled with arrays of
blkif_request_segment_aligned, this way we can send more segments in a
request.

The proposed implementation sets the maximum number of indirect grefs
(frames filled with blkif_request_segment_aligned) to 256 in the
backend and 32 in the frontend. The value in the frontend has been
chosen experimentally, and the backend value has been set to a sane
value that allows expanding the maximum number of indirect descriptors
in the frontend if needed.

The migration code has changed from the previous implementation, in
which we simply remapped the segments on the shared ring. Now the
maximum number of segments allowed in a request can change depending
on the backend, so we have to requeue all the requests in the ring and
in the queue and split the bios in them if they are bigger than the
new maximum number of segments.

[v2: Fixed minor comments by Konrad.
[v1: Added padding to make the indirect request 64bit aligned.
 Added some BUGs, comments; fixed number of indirect pages in
 blkif_get_x86_{32/64}_req. Added description about the indirect operation
 in blkif.h]
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
[v3: Fixed spaces and tabs mix ups]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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Roger Pau Monne authored and Konrad Rzeszutek Wilk committed Apr 18, 2013
1 parent 31552ee commit 402b27f
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Showing 5 changed files with 657 additions and 125 deletions.
134 changes: 98 additions & 36 deletions drivers/block/xen-blkback/blkback.c
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,7 @@
* IO workloads.
*/

static int xen_blkif_max_buffer_pages = 704;
static int xen_blkif_max_buffer_pages = 1024;
module_param_named(max_buffer_pages, xen_blkif_max_buffer_pages, int, 0644);
MODULE_PARM_DESC(max_buffer_pages,
"Maximum number of free pages to keep in each block backend buffer");
Expand All @@ -75,7 +75,7 @@ MODULE_PARM_DESC(max_buffer_pages,
* algorithm.
*/

static int xen_blkif_max_pgrants = 352;
static int xen_blkif_max_pgrants = 1056;
module_param_named(max_persistent_grants, xen_blkif_max_pgrants, int, 0644);
MODULE_PARM_DESC(max_persistent_grants,
"Maximum number of grants to map persistently");
Expand Down Expand Up @@ -636,10 +636,6 @@ int xen_blkif_schedule(void *arg)
return 0;
}

struct seg_buf {
unsigned int offset;
unsigned int nsec;
};
/*
* Unmap the grant references, and also remove the M2P over-rides
* used in the 'pending_req'.
Expand Down Expand Up @@ -818,29 +814,69 @@ static int xen_blkbk_map(struct xen_blkif *blkif, grant_ref_t grefs[],
return -ENOMEM;
}

static int xen_blkbk_map_seg(struct blkif_request *req,
struct pending_req *pending_req,
static int xen_blkbk_map_seg(struct pending_req *pending_req,
struct seg_buf seg[],
struct page *pages[])
{
int i, rc;
grant_ref_t grefs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
int rc;

for (i = 0; i < req->u.rw.nr_segments; i++)
grefs[i] = req->u.rw.seg[i].gref;

rc = xen_blkbk_map(pending_req->blkif, grefs,
rc = xen_blkbk_map(pending_req->blkif, pending_req->grefs,
pending_req->persistent_gnts,
pending_req->grant_handles, pending_req->pages,
req->u.rw.nr_segments,
pending_req->nr_pages,
(pending_req->operation != BLKIF_OP_READ));
if (rc)
return rc;

for (i = 0; i < req->u.rw.nr_segments; i++)
seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
return rc;
}

return 0;
static int xen_blkbk_parse_indirect(struct blkif_request *req,
struct pending_req *pending_req,
struct seg_buf seg[],
struct phys_req *preq)
{
struct persistent_gnt **persistent =
pending_req->indirect_persistent_gnts;
struct page **pages = pending_req->indirect_pages;
struct xen_blkif *blkif = pending_req->blkif;
int indirect_grefs, rc, n, nseg, i;
struct blkif_request_segment_aligned *segments = NULL;

nseg = pending_req->nr_pages;
indirect_grefs = INDIRECT_PAGES(nseg);
BUG_ON(indirect_grefs > BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST);

rc = xen_blkbk_map(blkif, req->u.indirect.indirect_grefs,
persistent, pending_req->indirect_handles,
pages, indirect_grefs, true);
if (rc)
goto unmap;

for (n = 0, i = 0; n < nseg; n++) {
if ((n % SEGS_PER_INDIRECT_FRAME) == 0) {
/* Map indirect segments */
if (segments)
kunmap_atomic(segments);
segments = kmap_atomic(pages[n/SEGS_PER_INDIRECT_FRAME]);
}
i = n % SEGS_PER_INDIRECT_FRAME;
pending_req->grefs[n] = segments[i].gref;
seg[n].nsec = segments[i].last_sect -
segments[i].first_sect + 1;
seg[n].offset = (segments[i].first_sect << 9);
if ((segments[i].last_sect >= (PAGE_SIZE >> 9)) ||
(segments[i].last_sect < segments[i].first_sect)) {
rc = -EINVAL;
goto unmap;
}
preq->nr_sects += seg[n].nsec;
}

unmap:
if (segments)
kunmap_atomic(segments);
xen_blkbk_unmap(blkif, pending_req->indirect_handles,
pages, persistent, indirect_grefs);
return rc;
}

static int dispatch_discard_io(struct xen_blkif *blkif,
Expand Down Expand Up @@ -1013,6 +1049,7 @@ __do_block_io_op(struct xen_blkif *blkif)
case BLKIF_OP_WRITE:
case BLKIF_OP_WRITE_BARRIER:
case BLKIF_OP_FLUSH_DISKCACHE:
case BLKIF_OP_INDIRECT:
if (dispatch_rw_block_io(blkif, &req, pending_req))
goto done;
break;
Expand Down Expand Up @@ -1059,17 +1096,28 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
struct pending_req *pending_req)
{
struct phys_req preq;
struct seg_buf seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct seg_buf *seg = pending_req->seg;
unsigned int nseg;
struct bio *bio = NULL;
struct bio *biolist[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct bio **biolist = pending_req->biolist;
int i, nbio = 0;
int operation;
struct blk_plug plug;
bool drain = false;
struct page **pages = pending_req->pages;
unsigned short req_operation;

req_operation = req->operation == BLKIF_OP_INDIRECT ?
req->u.indirect.indirect_op : req->operation;
if ((req->operation == BLKIF_OP_INDIRECT) &&
(req_operation != BLKIF_OP_READ) &&
(req_operation != BLKIF_OP_WRITE)) {
pr_debug(DRV_PFX "Invalid indirect operation (%u)\n",
req_operation);
goto fail_response;
}

switch (req->operation) {
switch (req_operation) {
case BLKIF_OP_READ:
blkif->st_rd_req++;
operation = READ;
Expand All @@ -1091,33 +1139,47 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
}

/* Check that the number of segments is sane. */
nseg = req->u.rw.nr_segments;
nseg = req->operation == BLKIF_OP_INDIRECT ?
req->u.indirect.nr_segments : req->u.rw.nr_segments;

if (unlikely(nseg == 0 && operation != WRITE_FLUSH) ||
unlikely(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
unlikely((req->operation != BLKIF_OP_INDIRECT) &&
(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) ||
unlikely((req->operation == BLKIF_OP_INDIRECT) &&
(nseg > MAX_INDIRECT_SEGMENTS))) {
pr_debug(DRV_PFX "Bad number of segments in request (%d)\n",
nseg);
/* Haven't submitted any bio's yet. */
goto fail_response;
}

preq.sector_number = req->u.rw.sector_number;
preq.nr_sects = 0;

pending_req->blkif = blkif;
pending_req->id = req->u.rw.id;
pending_req->operation = req->operation;
pending_req->operation = req_operation;
pending_req->status = BLKIF_RSP_OKAY;
pending_req->nr_pages = nseg;

for (i = 0; i < nseg; i++) {
seg[i].nsec = req->u.rw.seg[i].last_sect -
req->u.rw.seg[i].first_sect + 1;
if ((req->u.rw.seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
(req->u.rw.seg[i].last_sect < req->u.rw.seg[i].first_sect))
if (req->operation != BLKIF_OP_INDIRECT) {
preq.dev = req->u.rw.handle;
preq.sector_number = req->u.rw.sector_number;
for (i = 0; i < nseg; i++) {
pending_req->grefs[i] = req->u.rw.seg[i].gref;
seg[i].nsec = req->u.rw.seg[i].last_sect -
req->u.rw.seg[i].first_sect + 1;
seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
if ((req->u.rw.seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
(req->u.rw.seg[i].last_sect <
req->u.rw.seg[i].first_sect))
goto fail_response;
preq.nr_sects += seg[i].nsec;
}
} else {
preq.dev = req->u.indirect.handle;
preq.sector_number = req->u.indirect.sector_number;
if (xen_blkbk_parse_indirect(req, pending_req, seg, &preq))
goto fail_response;
preq.nr_sects += seg[i].nsec;

}

if (xen_vbd_translate(&preq, blkif, operation) != 0) {
Expand Down Expand Up @@ -1154,7 +1216,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
* the hypercall to unmap the grants - that is all done in
* xen_blkbk_unmap.
*/
if (xen_blkbk_map_seg(req, pending_req, seg, pages))
if (xen_blkbk_map_seg(pending_req, seg, pages))
goto fail_flush;

/*
Expand Down Expand Up @@ -1220,7 +1282,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
pending_req->nr_pages);
fail_response:
/* Haven't submitted any bio's yet. */
make_response(blkif, req->u.rw.id, req->operation, BLKIF_RSP_ERROR);
make_response(blkif, req->u.rw.id, req_operation, BLKIF_RSP_ERROR);
free_req(blkif, pending_req);
msleep(1); /* back off a bit */
return -EIO;
Expand Down
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