UBUNTU: SAUCE: Improve Amazon EBS performance for EC2
 

OriginalAuthor: Amazona from Ben Howard <behoward@amazon.com>
BugLink: http://bugs.launchpad.net/bugs/634316

The pv-ops kernel suffers from poor performance when using Amazon's
Elastic block storage (EBS). This patch from Amazon improves pv-ops
kernel performance, and has not exhibited any regressions.

Signed-off-by: John Johansen <john.johansen@canonical.com>
---
drivers/block/xen-blkfront.c | 125 +++++++++++++++++++++++++++-----------
include/xen/interface/io/blkif.h | 12 ++++
2 files changed, 101 insertions(+), 36 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index cda9b5a..221028a 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -69,7 +69,8 @@ struct blk_shadow {

static const struct block_device_operations xlvbd_block_fops;

-#define BLK_RING_SIZE __RING_SIZE((struct blkif_sring *)0, PAGE_SIZE)
+#define BLK_MAX_RING_AREA_SIZE (BLKIF_MAX_NUM_RING_PAGES * PAGE_SIZE)
+#define BLK_MAX_RING_SIZE __RING_SIZE((struct blkif_sring *)0, BLK_MAX_RING_AREA_SIZE)

/*
* We have one of these per vbd, whether ide, scsi or 'other'. They
@@ -83,14 +84,15 @@ struct blkfront_info
int vdevice;
blkif_vdev_t handle;
enum blkif_state connected;
- int ring_ref;
+ int num_ring_pages;
+ int ring_ref[BLKIF_MAX_NUM_RING_PAGES];
struct blkif_front_ring ring;
struct scatterlist sg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
unsigned int evtchn, irq;
struct request_queue *rq;
struct work_struct work;
struct gnttab_free_callback callback;
- struct blk_shadow shadow[BLK_RING_SIZE];
+ struct blk_shadow shadow[BLK_MAX_RING_SIZE];
unsigned long shadow_free;
int feature_barrier;
int is_ready;
@@ -104,8 +106,6 @@ struct blkfront_info

static DEFINE_SPINLOCK(blkif_io_lock);

-#define MAXIMUM_OUTSTANDING_BLOCK_REQS
- (BLKIF_MAX_SEGMENTS_PER_REQUEST * BLK_RING_SIZE)
#define GRANT_INVALID_REF 0

#define PARTS_PER_DISK 16
@@ -124,7 +124,8 @@ static DEFINE_SPINLOCK(blkif_io_lock);
static int get_id_from_freelist(struct blkfront_info *info)
{
unsigned long free = info->shadow_free;
- BUG_ON(free >= BLK_RING_SIZE);
+ int ring_size = __RING_SIZE((struct blkif_sring *)0, info->num_ring_pages * PAGE_SIZE);
+ BUG_ON(free >= ring_size);
info->shadow_free = info->shadow[free].req.id;
info->shadow[free].req.id = 0x0fffffee; /* debug */
return free;
@@ -496,6 +497,8 @@ static void blkif_restart_queue(struct work_struct *work)

static void blkif_free(struct blkfront_info *info, int suspend)
{
+ int i;
+
/* Prevent new requests being issued until we fix things up. */
spin_lock_irq(&blkif_io_lock);
info->connected = suspend ?
@@ -511,10 +514,17 @@ static void blkif_free(struct blkfront_info *info, int suspend)
flush_scheduled_work();

/* Free resources associated with old device channel. */
- if (info->ring_ref != GRANT_INVALID_REF) {
- gnttab_end_foreign_access(info->ring_ref, 0,
- (unsigned long)info->ring.sring);
- info->ring_ref = GRANT_INVALID_REF;
+ for (i=0;i<info->num_ring_pages;i++) {
+ /* Free resources associated with old device channel. */
+ if (info->ring_ref[i] != GRANT_INVALID_REF) {
+ gnttab_end_foreign_access(info->ring_ref[i], 0, 0L);
+ info->ring_ref[i] = GRANT_INVALID_REF;
+ }
+ }
+ if (info->ring.sring) {
+ int ring_area_size = info->num_ring_pages * PAGE_SIZE;
+ free_pages((unsigned long)info->ring.sring,
+ get_order(ring_area_size ));
info->ring.sring = NULL;
}
if (info->irq)
@@ -607,27 +617,32 @@ static int setup_blkring(struct xenbus_device *dev,
struct blkfront_info *info)
{
struct blkif_sring *sring;
- int err;
+ int i, order, err;
+ int ring_area_size = info->num_ring_pages * PAGE_SIZE;

- info->ring_ref = GRANT_INVALID_REF;
+ for (i=0;i<info->num_ring_pages; i++) {
+ info->ring_ref[i] = GRANT_INVALID_REF;
+ }

- sring = (struct blkif_sring *)__get_free_page(GFP_NOIO | __GFP_HIGH);
+ order = get_order(ring_area_size);
+ sring = (struct blkif_sring *)__get_free_pages(GFP_KERNEL, order);
if (!sring) {
xenbus_dev_fatal(dev, -ENOMEM, "allocating shared ring");
return -ENOMEM;
}
SHARED_RING_INIT(sring);
- FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);
-
- sg_init_table(info->sg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
-
- err = xenbus_grant_ring(dev, virt_to_mfn(info->ring.sring));
- if (err < 0) {
- free_page((unsigned long)sring);
- info->ring.sring = NULL;
- goto fail;
+ FRONT_RING_INIT(&info->ring, sring, ring_area_size);
+
+ for (i=0;i<info->num_ring_pages; i++) {
+ unsigned long addr = (unsigned long)info->ring.sring + i * PAGE_SIZE;
+ err = xenbus_grant_ring(dev, virt_to_mfn(addr));
+ if (err < 0) {
+ free_pages((unsigned long)sring, order);
+ info->ring.sring = NULL;
+ goto fail;
+ }
+ info->ring_ref[i] = err;
}
- info->ring_ref = err;

err = xenbus_alloc_evtchn(dev, &info->evtchn);
if (err)
@@ -656,8 +671,14 @@ static int talk_to_backend(struct xenbus_device *dev,
{
const char *message = NULL;
struct xenbus_transaction xbt;
- int err;
-
+ int err, i;
+
+ BUILD_BUG_ON(BLKIF_MAX_NUM_RING_PAGES != 1 &&
+ BLKIF_MAX_NUM_RING_PAGES != 2 &&
+ BLKIF_MAX_NUM_RING_PAGES != 4 &&
+ BLKIF_MAX_NUM_RING_PAGES != 8 &&
+ BLKIF_MAX_NUM_RING_PAGES != 16);
+
/* Create shared ring, alloc event channel. */
err = setup_blkring(dev, info);
if (err)
@@ -670,12 +691,31 @@ again:
goto destroy_blkring;
}

- err = xenbus_printf(xbt, dev->nodename,
- "ring-ref", "%u", info->ring_ref);
- if (err) {
- message = "writing ring-ref";
- goto abort_transaction;
- }
+ if (info->num_ring_pages == 1) {
+ err = xenbus_printf(xbt, dev->nodename,
+ "ring-ref","%u", info->ring_ref[0]);
+ if (err) {
+ message = "writing ring-ref";
+ goto abort_transaction;
+ }
+ } else {
+ err = xenbus_printf(xbt, dev->nodename, "num-ring-pages", "%u",
+ info->num_ring_pages);
+ if (err) {
+ message = "writing num-ring-pages";
+ goto abort_transaction;
+ }
+ for (i=0;i<info->num_ring_pages;i++) {
+ char buf[16];
+ snprintf(buf, sizeof(buf), "ring-ref%d", i);
+ err = xenbus_printf(xbt, dev->nodename, buf, "%u",
+ info->ring_ref[i]);
+ if (err) {
+ message = "writing ring-refs";
+ goto abort_transaction;
+ }
+ }
+ }
err = xenbus_printf(xbt, dev->nodename,
"event-channel", "%u", info->evtchn);
if (err) {
@@ -723,6 +763,7 @@ static int blkfront_probe(struct xenbus_device *dev,
{
int err, vdevice, i;
struct blkfront_info *info;
+ int ring_size, max_ring_pages;

/* FIXME: Use dynamic device id if this is not set. */
err = xenbus_scanf(XBT_NIL, dev->nodename,
@@ -736,6 +777,10 @@ static int blkfront_probe(struct xenbus_device *dev,
return err;
}
}
+ err = xenbus_scanf(XBT_NIL, dev->otherend,
+ "max-ring-pages", "%u", &max_ring_pages );
+ if (err != 1)
+ max_ring_pages = 1;

info = kzalloc(sizeof(*info), GFP_KERNEL);
if (!info) {
@@ -748,9 +793,13 @@ static int blkfront_probe(struct xenbus_device *dev,
info->connected = BLKIF_STATE_DISCONNECTED;
INIT_WORK(&info->work, blkif_restart_queue);

- for (i = 0; i < BLK_RING_SIZE; i++)
+ info->num_ring_pages = min(max_ring_pages, BLKIF_MAX_NUM_RING_PAGES);
+
+ ring_size = __RING_SIZE((struct blkif_sring *)0,
+ info->num_ring_pages * PAGE_SIZE);
+ for (i = 0; i < ring_size; i++)
info->shadow[i].req.id = i+1;
- info->shadow[BLK_RING_SIZE-1].req.id = 0x0fffffff;
+ info->shadow[ring_size-1].req.id = 0x0fffffff;

/* Front end dir is a number, which is used as the id. */
info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
@@ -763,6 +812,9 @@ static int blkfront_probe(struct xenbus_device *dev,
return err;
}

+ printk(KERN_INFO "blkfront %s num-ring-pages %d nr_ents %d.
",
+ dev->nodename, info->num_ring_pages, ring_size);
+
return 0;
}

@@ -773,6 +825,7 @@ static int blkif_recover(struct blkfront_info *info)
struct blkif_request *req;
struct blk_shadow *copy;
int j;
+ int ring_size = __RING_SIZE((struct blkif_sring *)0, info->num_ring_pages * PAGE_SIZE);

/* Stage 1: Make a safe copy of the shadow state. */
copy = kmalloc(sizeof(info->shadow),
@@ -783,13 +836,13 @@ static int blkif_recover(struct blkfront_info *info)

/* Stage 2: Set up free list. */
memset(&info->shadow, 0, sizeof(info->shadow));
- for (i = 0; i < BLK_RING_SIZE; i++)
+ for (i = 0; i < ring_size; i++)
info->shadow[i].req.id = i+1;
info->shadow_free = info->ring.req_prod_pvt;
- info->shadow[BLK_RING_SIZE-1].req.id = 0x0fffffff;
+ info->shadow[ring_size-1].req.id = 0x0fffffff;

/* Stage 3: Find pending requests and requeue them. */
- for (i = 0; i < BLK_RING_SIZE; i++) {
+ for (i = 0; i < ring_size; i++) {
/* Not in use? */
if (copy[i].request == 0)
continue;
diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h
index c2d1fa4..f7837ca 100644
--- a/include/xen/interface/io/blkif.h
+++ b/include/xen/interface/io/blkif.h
@@ -87,6 +87,18 @@ struct blkif_response {

DEFINE_RING_TYPES(blkif, struct blkif_request, struct blkif_response);

+/*
+ * Maximum number of pages used for a blkif ring
+ * max-ring-pages advertised by blkback to blkfront may be lowered at blkback
+ * mod load time. Load time param set to default.
+ */
+#define BLKIF_MAX_NUM_RING_PAGES 16
+#define BLKIF_MAX_NUM_RING_PAGES_DFLT 4
+#if BLKIF_MAX_NUM_RING_PAGES < BLKIF_MAX_NUM_RING_PAGES_DFLT
+#undef BLKIF_MAX_NUM_RING_PAGES_DFLT
+#define BLKIF_MAX_NUM_RING_PAGES_DFLT BLKIF_MAX_NUM_RING_PAGES
+#endif
+
#define VDISK_CDROM 0x1
#define VDISK_REMOVABLE 0x2
#define VDISK_READONLY 0x4
--
1.7.1


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