This patch implements persistent grants for the xen-blk{front,back}
mechanism. The effect of this change is to reduce the number of unmap
operations performed, since they cause a (costly) TLB shootdown. This
allows the I/O performance to scale better when a large number of VMs
are performing I/O.
Previously, the blkfront driver was supplied a bvec[] from the request
queue. This was granted to dom0; dom0 performed the I/O and wrote
directly into the grant-mapped memory and unmapped it; blkfront then
removed foreign access for that grant. The cost of unmapping scales
badly with the number of CPUs in Dom0. An experiment showed that when
Dom0 has 24 VCPUs, and guests are performing parallel I/O to a
ramdisk, the IPIs from performing unmap's is a bottleneck at 5 guests
(at which point 650,000 IOPS are being performed in total). If more
than 5 guests are used, the performance declines. By 10 guests, only
400,000 IOPS are being performed.
This patch improves performance by only unmapping when the connection
between blkfront and back is broken.
On startup, blk{front,back} use xenbus to communicate their ability to
perform 'feature-persistent'. Iff both ends have this ability,
persistent mode is used.
To perform a read, in persistent mode, blkfront uses a separate pool
of pages that it maps to dom0. When a request comes in, blkfront
transmutes the request so that blkback will write into one of these
free pages. Blkback keeps note of which grefs it has already
mapped. When a new ring request comes to blkback, it looks to see if
it has already mapped that page. If so, it will not map it again. If
the page hasn't been previously mapped, it is mapped now, and a record
is kept of this mapping. Blkback proceeds as usual. When blkfront is
notified that blkback has completed a request, it memcpy's from the
shared memory, into the bvec supplied. A record that the {gref, page}
tuple is mapped, and not inflight is kept.
Writes are similar, except that the memcpy is peformed from the
supplied bvecs, into the shared pages, before the request is put onto
the ring.
Blkback has to store a mapping of grefs=>{page mapped to by gref} in
an array. As the grefs are not known apriori, and provide no
guarantees on their ordering, we have to perform a linear search
through this array to find the page, for every gref we receive. The
overhead of this is low, however future work might want to use a more
efficient data structure to reduce this O(n) operation.
We (ijc, and myself) have introduced a new constant,
BLKIF_MAX_PERS_REQUESTS_PER_DEV. This is to prevent a malicious guest
from attempting a DoS, by supplying fresh grefs, causing the Dom0
kernel from to map excessively. This is currently set to 256---the
maximum number of entires in the ring. As the number of inflight
requests <= size of ring, 256 is also the maximum sensible size. This
introduces a maximum overhead of 11MB of mapped memory, per block
device. In practice, we don't typically use about 60 of these. If the
guest exceeds the 256 limit, it is either buggy or malicious. We treat
this in one of two ways:
1) If we have mapped <
BLKIF_MAX_SEGMENTS_PER_REQUEST * BLKIF_MAX_PERS_REQUESTS_PER_DEV
pages, we will persistently map the grefs. This can occur is previous
requests have not used all BLKIF_MAX_SEGMENTS_PER_REQUEST segments.
2) Otherwise, we revert to non-persistent grants for all future grefs.
In writing this patch, the question arrises as to if the additional
cost of performing memcpys in the guest (to/from the pool of granted
pages) outweigh the gains of not performing TLB shootdowns. The answer
to that question is `no'. There appears to be very little, if any
additional cost to the guest of using persistent grants. There is
perhaps a small saving, from the reduced number of hypercalls
performed in granting, and ending foreign access.
Signed-off-by: Oliver Chick <oliver.ch...@citrix.com>
---
drivers/block/xen-blkback/blkback.c | 149 +++++++++++++++++++++++++---
drivers/block/xen-blkback/common.h | 16 +++
drivers/block/xen-blkback/xenbus.c | 21 +++-
drivers/block/xen-blkfront.c | 186 ++++++++++++++++++++++++++++++-----
include/xen/interface/io/blkif.h | 9 ++
5 files changed, 338 insertions(+), 43 deletions(-)
diff --git a/drivers/block/xen-blkback/blkback.c
b/drivers/block/xen-blkback/blkback.c
index 73f196c..f95dee9 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -78,6 +78,7 @@ struct pending_req {
unsigned short operation;
int status;
struct list_head free_list;
+ u8 is_pers;
};
#define BLKBACK_INVALID_HANDLE (~0)
@@ -128,6 +129,24 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
static void make_response(struct xen_blkif *blkif, u64 id,
unsigned short op, int st);
+static void add_pers_gnt(struct pers_gnt *pers_gnt, struct xen_blkif *blkif)
+{
+ BUG_ON(blkif->pers_gnt_c >= BLKIF_MAX_PERS_REQUESTS_PER_DEV *
+ BLKIF_MAX_SEGMENTS_PER_REQUEST);
+ blkif->pers_gnts[blkif->pers_gnt_c++] = pers_gnt;
+}
+
+static struct pers_gnt *get_pers_gnt(struct xen_blkif *blkif,
+ grant_ref_t gref)
+{
+ int i;
+
+ for (i = 0; i < blkif->pers_gnt_c; i++)
+ if (gref == blkif->pers_gnts[i]->gnt)
+ return blkif->pers_gnts[i];
+ return NULL;
+}
+
/*
* Retrieve from the 'pending_reqs' a free pending_req structure to be used.
*/
@@ -274,6 +293,12 @@ int xen_blkif_schedule(void *arg)
{
struct xen_blkif *blkif = arg;
struct xen_vbd *vbd = &blkif->vbd;
+ struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct pers_gnt *pers_gnt;
+ int i;
+ int ret = 0;
+ int segs_to_unmap;
xen_blkif_get(blkif);
@@ -301,6 +326,29 @@ int xen_blkif_schedule(void *arg)
print_stats(blkif);
}
+ /* Free all persistent grant pages */
+
+ while (segs_to_unmap = min(BLKIF_MAX_SEGMENTS_PER_REQUEST,
+ blkif->pers_gnt_c)) {
+
+ for (i = 0; i < segs_to_unmap; i++) {
+ pers_gnt = blkif->pers_gnts[blkif->pers_gnt_c - i - 1];
+
+ gnttab_set_unmap_op(&unmap[i],
+ pfn_to_kaddr(page_to_pfn(
+ pers_gnt->page)),
+ GNTMAP_host_map,
+ pers_gnt->handle);
+
+ pages[i] = pers_gnt->page;
+ }
+
+ ret = gnttab_unmap_refs(unmap, pages, segs_to_unmap, false);
+ BUG_ON(ret);
+
+ blkif->pers_gnt_c -= segs_to_unmap;
+
+ }
+
if (log_stats)
print_stats(blkif);
@@ -343,13 +391,28 @@ static void xen_blkbk_unmap(struct pending_req *req)
static int xen_blkbk_map(struct blkif_request *req,
struct pending_req *pending_req,
- struct seg_buf seg[])
+ struct seg_buf seg[],
+ struct page *pages[])
{
struct gnttab_map_grant_ref map[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct pers_gnt *new_pers_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct pers_gnt *pers_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct page *pages_to_gnt[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct pers_gnt *pers_gnt;
+ phys_addr_t addr;
int i;
+ int new_map;
int nseg = req->u.rw.nr_segments;
+ int segs_to_init = 0;
int ret = 0;
+ int use_pers_gnts;
+ use_pers_gnts = (pending_req->blkif->can_grant_persist &&
+ pending_req->blkif->pers_gnt_c <
+ BLKIF_MAX_SEGMENTS_PER_REQUEST *
+ BLKIF_MAX_PERS_REQUESTS_PER_DEV);
+
+ pending_req->is_pers = use_pers_gnts;
/*
* Fill out preq.nr_sects with proper amount of sectors, and setup
* assign map[..] with the PFN of the page in our domain with the
@@ -358,36 +421,87 @@ static int xen_blkbk_map(struct blkif_request *req,
for (i = 0; i < nseg; i++) {
uint32_t flags;
+ if (use_pers_gnts) {
+ pers_gnt = get_pers_gnt(pending_req->blkif,
+ req->u.rw.seg[i].gref);
+ if (!pers_gnt) {
+ new_map = 1;
+ pers_gnt = kmalloc(sizeof(struct pers_gnt),
+ GFP_KERNEL);
+ if (!pers_gnt)
+ return -ENOMEM;
+ pers_gnt->page = alloc_page(GFP_KERNEL);
+ if (!pers_gnt->page)
+ return -ENOMEM;
+ pers_gnt->gnt = req->u.rw.seg[i].gref;
+
+ pages_to_gnt[segs_to_init] = pers_gnt->page;
+ new_pers_gnts[segs_to_init] = pers_gnt;
+
+ add_pers_gnt(pers_gnt, pending_req->blkif);
+
+ } else {
+ new_map = 0;
+ }
+ pages[i] = pers_gnt->page;
+ addr = (unsigned long) pfn_to_kaddr(
+ page_to_pfn(pers_gnt->page));
+ pers_gnts[i] = pers_gnt;
+ } else {
+ new_map = 1;
+ pages[i] = blkbk->pending_page(pending_req, i);
+ addr = vaddr(pending_req, i);
+ pages_to_gnt[i] = blkbk->pending_page(pending_req, i);
+ }
+
flags = GNTMAP_host_map;
- if (pending_req->operation != BLKIF_OP_READ)
+ if (!use_pers_gnts && (pending_req->operation != BLKIF_OP_READ))
flags |= GNTMAP_readonly;
- gnttab_set_map_op(&map[i], vaddr(pending_req, i), flags,
- req->u.rw.seg[i].gref,
- pending_req->blkif->domid);
+ if (new_map) {
+ gnttab_set_map_op(&map[segs_to_init++], addr,
+ flags, req->u.rw.seg[i].gref,
+ pending_req->blkif->domid);
+ }
}
- ret = gnttab_map_refs(map, NULL, &blkbk->pending_page(pending_req, 0),
nseg);
- BUG_ON(ret);
+ if (segs_to_init) {
+ ret = gnttab_map_refs(map, NULL, pages_to_gnt, segs_to_init);
+ BUG_ON(ret);
+ }
/*
* Now swizzle the MFN in our domain with the MFN from the other domain
* so that when we access vaddr(pending_req,i) it has the contents of
* the page from the other domain.
*/
- for (i = 0; i < nseg; i++) {
+ for (i = 0; i < segs_to_init; i++) {
if (unlikely(map[i].status != 0)) {
pr_debug(DRV_PFX "invalid buffer -- could not remap
it\n");
map[i].handle = BLKBACK_INVALID_HANDLE;
ret |= 1;
}
- pending_handle(pending_req, i) = map[i].handle;
+ if (use_pers_gnts) {
+ /* store the `out' values from map */
+ pending_req->blkif->pers_gnts
+ [pending_req->blkif->pers_gnt_c - segs_to_init +
+ i]->handle = map[i].handle;
+ new_pers_gnts[i]->dev_bus_addr = map[i].dev_bus_addr;
+ }
if (ret)
continue;
-
- seg[i].buf = map[i].dev_bus_addr |
- (req->u.rw.seg[i].first_sect << 9);
+ }
+ for (i = 0; i < nseg; i++) {
+ if (use_pers_gnts) {
+ pending_handle(pending_req, i) = pers_gnts[i]->handle;
+ seg[i].buf = pers_gnts[i]->dev_bus_addr |
+ (req->u.rw.seg[i].first_sect << 9);
+ } else {
+ pending_handle(pending_req, i) = map[i].handle;
+ seg[i].buf = map[i].dev_bus_addr |
+ (req->u.rw.seg[i].first_sect << 9);
+ }
}
return ret;
}
@@ -468,7 +582,8 @@ static void __end_block_io_op(struct pending_req
*pending_req, int error)
* the proper response on the ring.
*/
if (atomic_dec_and_test(&pending_req->pendcnt)) {
- xen_blkbk_unmap(pending_req);
+ if (!pending_req->is_pers)
+ xen_blkbk_unmap(pending_req);
make_response(pending_req->blkif, pending_req->id,
pending_req->operation, pending_req->status);
xen_blkif_put(pending_req->blkif);
@@ -590,6 +705,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
int operation;
struct blk_plug plug;
bool drain = false;
+ struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
switch (req->operation) {
case BLKIF_OP_READ:
@@ -676,7 +792,7 @@ 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(req, pending_req, seg))
+ if (xen_blkbk_map(req, pending_req, seg, pages))
goto fail_flush;
/*
@@ -688,7 +804,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
for (i = 0; i < nseg; i++) {
while ((bio == NULL) ||
(bio_add_page(bio,
- blkbk->pending_page(pending_req, i),
+ pages[i],
seg[i].nsec << 9,
seg[i].buf & ~PAGE_MASK) == 0)) {
@@ -743,7 +859,8 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
return 0;
fail_flush:
- xen_blkbk_unmap(pending_req);
+ if (!blkif->can_grant_persist)
+ xen_blkbk_unmap(pending_req);
fail_response:
/* Haven't submitted any bio's yet. */
make_response(blkif, req->u.rw.id, req->operation, BLKIF_RSP_ERROR);
diff --git a/drivers/block/xen-blkback/common.h
b/drivers/block/xen-blkback/common.h
index 9ad3b5e..1ecb709 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -47,6 +47,8 @@
#define DPRINTK(fmt, args...) \
pr_debug(DRV_PFX "(%s:%d) " fmt ".\n", \
__func__, __LINE__, ##args)
+#define BLKIF_MAX_PERS_REQUESTS_PER_DEV 256
+
/* Not a real protocol. Used to generate ring structs which contain
@@ -164,6 +166,14 @@ struct xen_vbd {
struct backend_info;
+
+struct pers_gnt {
+ struct page *page;
+ grant_ref_t gnt;
+ uint32_t handle;
+ uint64_t dev_bus_addr;
+};
+
struct xen_blkif {
/* Unique identifier for this interface. */
domid_t domid;
@@ -190,6 +200,12 @@ struct xen_blkif {
struct task_struct *xenblkd;
unsigned int waiting_reqs;
+ /* frontend feature information */
+ u8 can_grant_persist:1;
+ struct pers_gnt *pers_gnts[BLKIF_MAX_PERS_REQUESTS_PER_DEV *
+ BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ unsigned int pers_gnt_c;
+
/* statistics */
unsigned long st_print;
int st_rd_req;
diff --git a/drivers/block/xen-blkback/xenbus.c
b/drivers/block/xen-blkback/xenbus.c
index 4f66171..dc58cc4 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -681,6 +681,13 @@ again:
goto abort;
}
+ err = xenbus_printf(xbt, dev->nodename, "feature-persistent-grants",
+ "%d", 1);
+ if (err) {
+ xenbus_dev_fatal(dev, err, "writing persistent capability");
+ goto abort;
+ }
+
/* FIXME: use a typename instead */
err = xenbus_printf(xbt, dev->nodename, "info", "%u",
be->blkif->vbd.type |
@@ -721,6 +728,7 @@ static int connect_ring(struct backend_info *be)
struct xenbus_device *dev = be->dev;
unsigned long ring_ref;
unsigned int evtchn;
+ u8 pers_grants;
char protocol[64] = "";
int err;
@@ -750,8 +758,17 @@ static int connect_ring(struct backend_info *be)
xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
return -1;
}
- pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s)\n",
- ring_ref, evtchn, be->blkif->blk_protocol, protocol);
+ err = xenbus_gather(XBT_NIL, dev->otherend,
+ "feature-persistent-grants", "%d",
+ &pers_grants, NULL);
+ if (err)
+ pers_grants = 0;
+
+ be->blkif->can_grant_persist = pers_grants;
+
+ pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s)
persistent %d\n",
+ ring_ref, evtchn, be->blkif->blk_protocol, protocol,
+ pers_grants);
/* Map the shared frame, irq etc. */
err = xen_blkif_map(be->blkif, ring_ref, evtchn);
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index e4fb337..c1cc5fe 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -68,6 +68,13 @@ struct blk_shadow {
struct blkif_request req;
struct request *request;
unsigned long frame[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct gnt_list *grants_used[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+};
+
+struct gnt_list {
+ grant_ref_t gref;
+ unsigned long frame;
+ struct gnt_list *tail;
};
static DEFINE_MUTEX(blkfront_mutex);
@@ -97,11 +104,14 @@ struct blkfront_info
struct work_struct work;
struct gnttab_free_callback callback;
struct blk_shadow shadow[BLK_RING_SIZE];
+ struct gnt_list *persistent_grants_front;
+ unsigned int persistent_grants_c;
unsigned long shadow_free;
unsigned int feature_flush;
unsigned int flush_op;
unsigned int feature_discard:1;
unsigned int feature_secdiscard:1;
+ unsigned int feature_persistent:1;
unsigned int discard_granularity;
unsigned int discard_alignment;
int is_ready;
@@ -286,22 +296,37 @@ static int blkif_queue_request(struct request *req)
struct blkif_request *ring_req;
unsigned long id;
unsigned int fsect, lsect;
- int i, ref;
+ int i, ref, use_pers_gnts, new_pers_gnts;
grant_ref_t gref_head;
+ struct bio_vec *bvecs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct bio_vec *bvec;
+ struct req_iterator iter;
+ char *bvec_data;
+ void *shared_data;
+ unsigned long flags;
+ struct page *shared_page;
+ struct gnt_list *gnt_list_entry;
struct scatterlist *sg;
if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
return 1;
- if (gnttab_alloc_grant_references(
- BLKIF_MAX_SEGMENTS_PER_REQUEST, &gref_head) < 0) {
- gnttab_request_free_callback(
- &info->callback,
- blkif_restart_queue_callback,
- info,
- BLKIF_MAX_SEGMENTS_PER_REQUEST);
- return 1;
+ use_pers_gnts = info->feature_persistent;
+
+ if (info->persistent_grants_c < BLKIF_MAX_SEGMENTS_PER_REQUEST) {
+ new_pers_gnts = 1;
+ if (gnttab_alloc_grant_references(
+ BLKIF_MAX_SEGMENTS_PER_REQUEST, &gref_head) < 0) {
+ gnttab_request_free_callback(
+ &info->callback,
+ blkif_restart_queue_callback,
+ info,
+ BLKIF_MAX_SEGMENTS_PER_REQUEST);
+ return 1;
+ }
} else
+ new_pers_gnts = 0;
/* Fill out a communications ring structure. */
ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
@@ -341,20 +366,66 @@ static int blkif_queue_request(struct request *req)
BLKIF_MAX_SEGMENTS_PER_REQUEST);
for_each_sg(info->sg, sg, ring_req->u.rw.nr_segments, i) {
- buffer_mfn = pfn_to_mfn(page_to_pfn(sg_page(sg)));
fsect = sg->offset >> 9;
lsect = fsect + (sg->length >> 9) - 1;
- /* install a grant reference. */
- ref = gnttab_claim_grant_reference(&gref_head);
- BUG_ON(ref == -ENOSPC);
- gnttab_grant_foreign_access_ref(
+ if (use_pers_gnts && info->persistent_grants_c) {
+ gnt_list_entry = info->persistent_grants_front;
+
+ info->persistent_grants_front =
+ info->persistent_grants_front->tail;
+ ref = gnt_list_entry->gref;
+ buffer_mfn = pfn_to_mfn(gnt_list_entry->frame);
+ info->persistent_grants_c--;
+ } else {
+ ref = gnttab_claim_grant_reference(&gref_head);
+ BUG_ON(ref == -ENOSPC);
+
+ if (use_pers_gnts) {
+ gnt_list_entry =
+ kmalloc(sizeof(struct gnt_list),
+ GFP_ATOMIC);
+ if (!gnt_list_entry)
+ return -ENOMEM;
+
+ shared_page = alloc_page(GFP_ATOMIC);
+ if (!shared_page)
+ return -ENOMEM;
+
+ gnt_list_entry->frame =
+ page_to_pfn(shared_page);
+ gnt_list_entry->gref = ref;
+ } else
+ shared_page = sg_page(sg);
+
+ buffer_mfn = pfn_to_mfn(page_to_pfn(
+ shared_page));
+ gnttab_grant_foreign_access_ref(
ref,
info->xbdev->otherend_id,
buffer_mfn,
- rq_data_dir(req));
+ !use_pers_gnts && rq_data_dir(req));
+ }
+
+ if (use_pers_gnts)
+ info->shadow[id].grants_used[i] =
+ gnt_list_entry;
+
+ if (use_pers_gnts && rq_data_dir(req)) {
+ shared_data = kmap_atomic(
+ pfn_to_page(gnt_list_entry->frame));
+ bvec_data = kmap_atomic(sg_page(sg));
+
+ memcpy(shared_data + sg->offset,
+ bvec_data + sg->offset,
+ sg->length);
+
+ kunmap_atomic(bvec_data);
+ kunmap_atomic(shared_data);
+ }
info->shadow[id].frame[i] = mfn_to_pfn(buffer_mfn);
+
ring_req->u.rw.seg[i] =
(struct blkif_request_segment) {
.gref = ref,
@@ -368,7 +439,8 @@ static int blkif_queue_request(struct request *req)
/* Keep a private copy so we can reissue requests when recovering. */
info->shadow[id].req = *ring_req;
- gnttab_free_grant_references(gref_head);
+ if (new_pers_gnts)
+ gnttab_free_grant_references(gref_head);
return 0;
}
@@ -480,12 +552,13 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16
sector_size)
static void xlvbd_flush(struct blkfront_info *info)
{
blk_queue_flush(info->rq, info->feature_flush);
- printk(KERN_INFO "blkfront: %s: %s: %s\n",
+ printk(KERN_INFO "blkfront: %s: %s: %s. Persistent=%d\n",
info->gd->disk_name,
info->flush_op == BLKIF_OP_WRITE_BARRIER ?
"barrier" : (info->flush_op == BLKIF_OP_FLUSH_DISKCACHE ?
"flush diskcache" : "barrier or flush"),
- info->feature_flush ? "enabled" : "disabled");
+ info->feature_flush ? "enabled" : "disabled",
+ info->feature_persistent);
}
static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
@@ -707,6 +780,8 @@ static void blkif_restart_queue(struct work_struct *work)
static void blkif_free(struct blkfront_info *info, int suspend)
{
+ struct gnt_list *pers_gnt;
+
/* Prevent new requests being issued until we fix things up. */
spin_lock_irq(&info->io_lock);
info->connected = suspend ?
@@ -714,6 +789,15 @@ static void blkif_free(struct blkfront_info *info, int
suspend)
/* No more blkif_request(). */
if (info->rq)
blk_stop_queue(info->rq);
+
+ /* Remove all persistent grants */
+ while (info->persistent_grants_front) {
+ pers_gnt = info->persistent_grants_front;
+ info->persistent_grants_front = pers_gnt->tail;
+ gnttab_end_foreign_access(pers_gnt->gref, 0, 0UL);
+ kfree(pers_gnt);
+ }
+
/* No more gnttab callback work. */
gnttab_cancel_free_callback(&info->callback);
spin_unlock_irq(&info->io_lock);
@@ -734,13 +818,44 @@ static void blkif_free(struct blkfront_info *info, int
suspend)
}
-static void blkif_completion(struct blk_shadow *s)
+static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
+ struct blkif_response *bret)
{
int i;
- /* Do not let BLKIF_OP_DISCARD as nr_segment is in the same place
- * flag. */
- for (i = 0; i < s->req.u.rw.nr_segments; i++)
- gnttab_end_foreign_access(s->req.u.rw.seg[i].gref, 0, 0UL);
+ struct gnt_list *new_gnt_list_entry;
+ struct bio_vec *bvec;
+ struct req_iterator iter;
+ unsigned long flags;
+ char *bvec_data;
+ void *shared_data;
+
+ i = 0;
+ if (info->feature_persistent == 0) {
+ /* Do not let BLKIF_OP_DISCARD as nr_segment is in the same
+ * place flag. */
+ for (i = 0; i < s->req.u.rw.nr_segments; i++)
+ gnttab_end_foreign_access(s->req.u.rw.seg[i].gref,
+ 0, 0UL);
+ return;
+ }
+
+ if (bret->operation == BLKIF_OP_READ)
+ rq_for_each_segment(bvec, s->request, iter) {
+ shared_data = kmap_atomic
+ (pfn_to_page(s->grants_used[i++]->frame));
+ bvec_data = bvec_kmap_irq(bvec, &flags);
+ memcpy(bvec_data, shared_data + bvec->bv_offset,
+ bvec->bv_len);
+ bvec_kunmap_irq(bvec_data, &flags);
+ kunmap_atomic(shared_data);
+ }
+ /* Add the persistent grant into the list of free grants */
+ for (i = 0; i < s->req.u.rw.nr_segments; i++) {
+ new_gnt_list_entry = s->grants_used[i];
+ new_gnt_list_entry->tail = info->persistent_grants_front;
+ info->persistent_grants_front = new_gnt_list_entry;
+ info->persistent_grants_c++;
+ }
}
static irqreturn_t blkif_interrupt(int irq, void *dev_id)
@@ -783,7 +898,7 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
req = info->shadow[id].request;
if (bret->operation != BLKIF_OP_DISCARD)
- blkif_completion(&info->shadow[id]);
+ blkif_completion(&info->shadow[id], info, bret);
if (add_id_to_freelist(info, id)) {
WARN(1, "%s: response to %s (id %ld) couldn't be
recycled!\n",
@@ -943,6 +1058,12 @@ again:
message = "writing protocol";
goto abort_transaction;
}
+ err = xenbus_printf(xbt, dev->nodename,
+ "feature-persistent-grants", "%d", 1);
+ if (err) {
+ message = "Writing persistent grants front feature";
+ goto abort_transaction;
+ }
err = xenbus_transaction_end(xbt, 0);
if (err) {
@@ -1030,6 +1151,7 @@ static int blkfront_probe(struct xenbus_device *dev,
spin_lock_init(&info->io_lock);
info->xbdev = dev;
info->vdevice = vdevice;
+ info->persistent_grants_c = 0;
info->connected = BLKIF_STATE_DISCONNECTED;
INIT_WORK(&info->work, blkif_restart_queue);
@@ -1094,6 +1216,7 @@ static int blkif_recover(struct blkfront_info *info)
req->u.rw.seg[j].gref,
info->xbdev->otherend_id,
pfn_to_mfn(info->shadow[req->u.rw.id].frame[j]),
+ !info->feature_persistent &&
rq_data_dir(info->shadow[req->u.rw.id].request));
}
info->shadow[req->u.rw.id].req = *req;
@@ -1226,7 +1349,7 @@ static void blkfront_connect(struct blkfront_info *info)
unsigned long sector_size;
unsigned int binfo;
int err;
- int barrier, flush, discard;
+ int barrier, flush, discard, persistent;
switch (info->connected) {
case BLKIF_STATE_CONNECTED:
@@ -1297,6 +1420,19 @@ static void blkfront_connect(struct blkfront_info *info)
info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
}
+ /*
+ * Are we dealing with an old blkback that will unmap
+ * all grefs?
+ */
+ err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+ "feature-persistent-grants", "%d", &persistent,
+ NULL);
+
+ if (err)
+ info->feature_persistent = 0;
+ else
+ info->feature_persistent = persistent;
+
err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
"feature-discard", "%d", &discard,
NULL);
diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h
index ee338bf..cd267a9b 100644
--- a/include/xen/interface/io/blkif.h
+++ b/include/xen/interface/io/blkif.h
@@ -109,6 +109,15 @@ typedef uint64_t blkif_sector_t;
*/
#define BLKIF_MAX_SEGMENTS_PER_REQUEST 11
+/*
+ * Maximum number of persistent grants that can be mapped by Dom0 for each
+ * interface. This is set to be the size of the ring, as this is a limit on
+ * the number of requests that can be inflight at any one time. 256 imposes
+ * an overhead of 11MB of mapped kernel space per interface.
+ */
+#define BLKIF_MAX_PERS_REQUESTS_PER_DEV 256
+
+
struct blkif_request_rw {
uint8_t nr_segments; /* number of segments */
blkif_vdev_t handle; /* only for read/write requests */
--
1.7.9.5
--
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