> Background: Barriers are needed to make journaling filesystems work
> reliable. For some requests they need order constrains to make the
> transactions work correctly. Barrier requests are used to pass that
> ordering information to the block layer and/or to the device, so the
> constrains are obeyed when reordering requests for better write
> performance.
Just so I'm clear, this is just an optimization, right? -- linux does
the right thing without blk device barrier support, it just gives the
opportunity for more block scheduling flexibility (which is certainly a
good thing)
Out of interest, have you any benchmarks showing the benefits of barrier
support? I'd be very interested to see them.
Also, have you thought how this would work with blktap? Does the AIO
interface allow ordering constraints to be communicated to the kernel?
Thanks,
Ian
> Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxx>
> ---
> linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c | 41
> ++++++++++++++-----
> linux-2.6-xen-sparse/drivers/xen/blkback/common.h | 3 +
> linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c | 2
> linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c | 31
++++++++++++++
> linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c | 30
+++++++++++--
> linux-2.6-xen-sparse/drivers/xen/blkfront/block.h | 2
> linux-2.6-xen-sparse/drivers/xen/blkfront/vbd.c | 20 ++++++++-
> xen/include/public/io/blkif.h | 10 ++--
> 8 files changed, 117 insertions(+), 22 deletions(-)
>
> Index: build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkback/blkback.c
> ===================================================================
> --- build-64-unstable-11724.orig/linux-2.6-xen-
> sparse/drivers/xen/blkback/blkback.c
> +++ build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkback/blkback.c
> @@ -189,9 +189,9 @@ static void fast_flush_area(pending_req_
>
> static void print_stats(blkif_t *blkif)
> {
> - printk(KERN_DEBUG "%s: oo %3d | rd %4d | wr %4d\n",
> + printk(KERN_DEBUG "%s: oo %3d | rd %4d | wr %4d | br
%4d\n",
> current->comm, blkif->st_oo_req,
> - blkif->st_rd_req, blkif->st_wr_req);
> + blkif->st_rd_req, blkif->st_wr_req, blkif->st_br_req);
> blkif->st_print = jiffies + msecs_to_jiffies(10 * 1000);
> blkif->st_rd_req = 0;
> blkif->st_wr_req = 0;
> @@ -241,12 +241,17 @@ int blkif_schedule(void *arg)
> * COMPLETION CALLBACK -- Called as bh->b_end_io()
> */
>
> -static void __end_block_io_op(pending_req_t *pending_req, int
uptodate)
> +static void __end_block_io_op(pending_req_t *pending_req, int error)
> {
> /* An error fails the entire request. */
> - if (!uptodate) {
> - DPRINTK("Buffer not up-to-date at end of operation\n");
> + if (error) {
> + DPRINTK("Buffer not up-to-date at end of operation,
> error=%d\n", error);
> pending_req->status = BLKIF_RSP_ERROR;
> + if (pending_req->operation == BLKIF_OP_WRITE_BARRIER &&
error
> == -EOPNOTSUPP) {
> + pending_req->status = BLKIF_RSP_EOPNOTSUPP;
> + blkback_barrier(pending_req->blkif->be, 0);
> + printk("blkback: write barrier op failed, not
> supported\n");
> + }
> }
>
> if (atomic_dec_and_test(&pending_req->pendcnt)) {
> @@ -262,7 +267,7 @@ static int end_block_io_op(struct bio *b
> {
> if (bio->bi_size != 0)
> return 1;
> - __end_block_io_op(bio->bi_private, !error);
> + __end_block_io_op(bio->bi_private, error);
> bio_put(bio);
> return error;
> }
> @@ -319,6 +324,9 @@ static int do_block_io_op(blkif_t *blkif
> blkif->st_rd_req++;
> dispatch_rw_block_io(blkif, req, pending_req);
> break;
> + case BLKIF_OP_WRITE_BARRIER:
> + blkif->st_br_req++;
> + /* fall through */
> case BLKIF_OP_WRITE:
> blkif->st_wr_req++;
> dispatch_rw_block_io(blkif, req, pending_req);
> @@ -340,7 +348,6 @@ static void dispatch_rw_block_io(blkif_t
> pending_req_t *pending_req)
> {
> extern void ll_rw_block(int rw, int nr, struct buffer_head *
bhs[]);
> - int operation = (req->operation == BLKIF_OP_WRITE) ? WRITE :
READ;
> struct gnttab_map_grant_ref map[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> struct phys_req preq;
> struct {
> @@ -349,6 +356,22 @@ static void dispatch_rw_block_io(blkif_t
> unsigned int nseg;
> struct bio *bio = NULL,
*biolist[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> int ret, i, nbio = 0;
> + int operation;
> +
> + switch (req->operation) {
> + case BLKIF_OP_READ:
> + operation = READ;
> + break;
> + case BLKIF_OP_WRITE:
> + operation = WRITE;
> + break;
> + case BLKIF_OP_WRITE_BARRIER:
> + operation = WRITE_BARRIER;
> + break;
> + default:
> + operation = 0; /* make gcc happy */
> + BUG();
> + }
>
> /* Check that number of segments is sane. */
> nseg = req->nr_segments;
> @@ -364,7 +387,7 @@ static void dispatch_rw_block_io(blkif_t
>
> pending_req->blkif = blkif;
> pending_req->id = req->id;
> - pending_req->operation = operation;
> + pending_req->operation = req->operation;
> pending_req->status = BLKIF_RSP_OKAY;
> pending_req->nr_pages = nseg;
>
> @@ -380,7 +403,7 @@ static void dispatch_rw_block_io(blkif_t
> preq.nr_sects += seg[i].nsec;
>
> flags = GNTMAP_host_map;
> - if ( operation == WRITE )
> + if ( operation != READ )
> flags |= GNTMAP_readonly;
> gnttab_set_map_op(&map[i], vaddr(pending_req, i), flags,
> req->seg[i].gref, blkif->domid);
> Index: build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkback/common.h
> ===================================================================
> --- build-64-unstable-11724.orig/linux-2.6-xen-
> sparse/drivers/xen/blkback/common.h
> +++ build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkback/common.h
> @@ -87,6 +87,7 @@ typedef struct blkif_st {
> int st_rd_req;
> int st_wr_req;
> int st_oo_req;
> + int st_br_req;
>
> wait_queue_head_t waiting_to_free;
>
> @@ -131,4 +132,6 @@ void blkif_xenbus_init(void);
> irqreturn_t blkif_be_int(int irq, void *dev_id, struct pt_regs
*regs);
> int blkif_schedule(void *arg);
>
> +int blkback_barrier(struct backend_info *be, int state);
> +
> #endif /* __BLKIF__BACKEND__COMMON_H__ */
> Index: build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkback/xenbus.c
> ===================================================================
> --- build-64-unstable-11724.orig/linux-2.6-xen-
> sparse/drivers/xen/blkback/xenbus.c
> +++ build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkback/xenbus.c
> @@ -91,11 +91,13 @@ static void update_blkif_status(blkif_t
> VBD_SHOW(oo_req, "%d\n", be->blkif->st_oo_req);
> VBD_SHOW(rd_req, "%d\n", be->blkif->st_rd_req);
> VBD_SHOW(wr_req, "%d\n", be->blkif->st_wr_req);
> +VBD_SHOW(br_req, "%d\n", be->blkif->st_br_req);
>
> static struct attribute *vbdstat_attrs[] = {
> &dev_attr_oo_req.attr,
> &dev_attr_rd_req.attr,
> &dev_attr_wr_req.attr,
> + &dev_attr_br_req.attr,
> NULL
> };
>
> @@ -165,6 +167,31 @@ static int blkback_remove(struct xenbus_
> return 0;
> }
>
> +int blkback_barrier(struct backend_info *be, int state)
> +{
> + struct xenbus_device *dev = be->dev;
> + struct xenbus_transaction xbt;
> + int err;
> +
> + do {
> + err = xenbus_transaction_start(&xbt);
> + if (err) {
> + xenbus_dev_fatal(dev, err, "starting
transaction");
> + return -1;
> + }
> +
> + err = xenbus_printf(xbt, dev->nodename,
"feature-barrier",
> + "%d", state);
> + if (err) {
> + xenbus_transaction_end(xbt, 1);
> + xenbus_dev_fatal(dev, err, "writing
feature-barrier");
> + return -1;
> + }
> +
> + err = xenbus_transaction_end(xbt, 0);
> + } while (err == -EAGAIN);
> + return 0;
> +}
>
> /**
> * Entry point to this code when a new device is created. Allocate
the
> basic
> @@ -201,6 +228,10 @@ static int blkback_probe(struct xenbus_d
> if (err)
> goto fail;
>
> + err = blkback_barrier(be, 1);
> + if (err)
> + goto fail;
> +
> err = xenbus_switch_state(dev, XenbusStateInitWait);
> if (err)
> goto fail;
> Index: build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkfront/blkfront.c
> ===================================================================
> --- build-64-unstable-11724.orig/linux-2.6-xen-
> sparse/drivers/xen/blkfront/blkfront.c
> +++ build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkfront/blkfront.c
> @@ -316,6 +316,12 @@ static void connect(struct blkfront_info
> return;
> }
>
> + err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
> + "feature-barrier", "%lu",
&info->feature_barrier,
> + NULL);
> + if (err)
> + info->feature_barrier = 0;
> +
> err = xlvbd_add(sectors, info->vdevice, binfo, sector_size,
info);
> if (err) {
> xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
> @@ -544,11 +550,14 @@ static int blkif_queue_request(struct re
> info->shadow[id].request = (unsigned long)req;
>
> ring_req->id = id;
> - ring_req->operation = rq_data_dir(req) ?
> - BLKIF_OP_WRITE : BLKIF_OP_READ;
> ring_req->sector_number = (blkif_sector_t)req->sector;
> ring_req->handle = info->handle;
>
> + ring_req->operation = rq_data_dir(req) ?
> + BLKIF_OP_WRITE : BLKIF_OP_READ;
> + if (blk_barrier_rq(req))
> + ring_req->operation = BLKIF_OP_WRITE_BARRIER;
> +
> ring_req->nr_segments = 0;
> rq_for_each_bio (bio, req) {
> bio_for_each_segment (bvec, bio, idx) {
> @@ -645,6 +654,7 @@ static irqreturn_t blkif_int(int irq, vo
> RING_IDX i, rp;
> unsigned long flags;
> struct blkfront_info *info = (struct blkfront_info *)dev_id;
> + int uptodate;
>
> spin_lock_irqsave(&blkif_io_lock, flags);
>
> @@ -669,19 +679,27 @@ static irqreturn_t blkif_int(int irq, vo
>
> ADD_ID_TO_FREELIST(info, id);
>
> + uptodate = (bret->status == BLKIF_RSP_OKAY);
> switch (bret->operation) {
> + case BLKIF_OP_WRITE_BARRIER:
> + if (unlikely(bret->status ==
BLKIF_RSP_EOPNOTSUPP)) {
> + printk("blkfront: %s: write barrier op
failed\n",
> + info->gd->disk_name);
> + uptodate = -EOPNOTSUPP;
> + info->feature_barrier = 0;
> + xlvbd_barrier(info);
> + }
> + /* fall through */
> case BLKIF_OP_READ:
> case BLKIF_OP_WRITE:
> if (unlikely(bret->status != BLKIF_RSP_OKAY))
> DPRINTK("Bad return from blkdev data "
> "request: %x\n", bret->status);
>
> - ret = end_that_request_first(
> - req, (bret->status == BLKIF_RSP_OKAY),
> + ret = end_that_request_first(req, uptodate,
> req->hard_nr_sectors);
> BUG_ON(ret);
> - end_that_request_last(
> - req, (bret->status == BLKIF_RSP_OKAY));
> + end_that_request_last(req, uptodate);
> break;
> default:
> BUG();
> Index: build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkfront/block.h
> ===================================================================
> --- build-64-unstable-11724.orig/linux-2.6-xen-
> sparse/drivers/xen/blkfront/block.h
> +++ build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkfront/block.h
> @@ -126,6 +126,7 @@ struct blkfront_info
> struct gnttab_free_callback callback;
> struct blk_shadow shadow[BLK_RING_SIZE];
> unsigned long shadow_free;
> + int feature_barrier;
>
> /**
> * The number of people holding this device open. We won't
allow a
> @@ -152,5 +153,6 @@ extern void do_blkif_request (request_qu
> int xlvbd_add(blkif_sector_t capacity, int device,
> u16 vdisk_info, u16 sector_size, struct blkfront_info
*info);
> void xlvbd_del(struct blkfront_info *info);
> +int xlvbd_barrier(struct blkfront_info *info);
>
> #endif /* __XEN_DRIVERS_BLOCK_H__ */
> Index: build-64-unstable-11724/xen/include/public/io/blkif.h
> ===================================================================
> --- build-64-unstable-11724.orig/xen/include/public/io/blkif.h
> +++ build-64-unstable-11724/xen/include/public/io/blkif.h
> @@ -29,8 +29,9 @@
> #endif
> #define blkif_sector_t uint64_t
>
> -#define BLKIF_OP_READ 0
> -#define BLKIF_OP_WRITE 1
> +#define BLKIF_OP_READ 0
> +#define BLKIF_OP_WRITE 1
> +#define BLKIF_OP_WRITE_BARRIER 2
>
> /*
> * Maximum scatter/gather segments per request.
> @@ -61,8 +62,9 @@ struct blkif_response {
> };
> typedef struct blkif_response blkif_response_t;
>
> -#define BLKIF_RSP_ERROR -1 /* non-specific 'error' */
> -#define BLKIF_RSP_OKAY 0 /* non-specific 'okay' */
> +#define BLKIF_RSP_EOPNOTSUPP -2 /* operation not supported (can
happen on
> barrier writes) */
> +#define BLKIF_RSP_ERROR -1 /* non-specific 'error' */
> +#define BLKIF_RSP_OKAY 0 /* non-specific 'okay' */
>
> /*
> * Generate blkif ring structures and types.
> Index: build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkfront/vbd.c
> ===================================================================
> --- build-64-unstable-11724.orig/linux-2.6-xen-
> sparse/drivers/xen/blkfront/vbd.c
> +++
build-64-unstable-11724/linux-2.6-xen-sparse/drivers/xen/blkfront/vbd.c
> @@ -257,6 +257,10 @@ xlvbd_alloc_gendisk(int minor, blkif_sec
> }
>
> info->rq = gd->queue;
> + info->gd = gd;
> +
> + if (info->feature_barrier)
> + xlvbd_barrier(info);
>
> if (vdisk_info & VDISK_READONLY)
> set_disk_ro(gd, 1);
> @@ -267,8 +271,6 @@ xlvbd_alloc_gendisk(int minor, blkif_sec
> if (vdisk_info & VDISK_CDROM)
> gd->flags |= GENHD_FL_CD;
>
> - info->gd = gd;
> -
> return 0;
>
> out:
> @@ -316,3 +318,17 @@ xlvbd_del(struct blkfront_info *info)
> blk_cleanup_queue(info->rq);
> info->rq = NULL;
> }
> +
> +int
> +xlvbd_barrier(struct blkfront_info *info)
> +{
> + int err;
> +
> + err = blk_queue_ordered(info->rq,
> + info->feature_barrier ? QUEUE_ORDERED_DRAIN :
> QUEUE_ORDERED_NONE, NULL);
> + if (err)
> + return err;
> + printk("blkfront: %s: barriers %s\n",
> + info->gd->disk_name, info->feature_barrier ? "enabled" :
> "disabled");
> + return 0;
> +}
> Index: build-64-unstable-11724/linux-2.6-xen-
> sparse/drivers/xen/blkback/vbd.c
> ===================================================================
> --- build-64-unstable-11724.orig/linux-2.6-xen-
> sparse/drivers/xen/blkback/vbd.c
> +++
build-64-unstable-11724/linux-2.6-xen-sparse/drivers/xen/blkback/vbd.c
> @@ -104,7 +104,7 @@ int vbd_translate(struct phys_req *req,
> struct vbd *vbd = &blkif->vbd;
> int rc = -EACCES;
>
> - if ((operation == WRITE) && vbd->readonly)
> + if ((operation != READ) && vbd->readonly)
> goto out;
>
> if (unlikely((req->sector_number + req->nr_sects) >
vbd_sz(vbd)))
>
> --
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
Home