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xen-blkback: make the queue of free requests per backend
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Remove the last dependency from blkbk by moving the list of free
requests to blkif. This change reduces the contention on the list of
available requests.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: xen-devel@lists.xen.org
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 bb6acb2 commit bf0720c
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Showing 3 changed files with 74 additions and 105 deletions.
123 changes: 18 additions & 105 deletions drivers/block/xen-blkback/blkback.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -49,20 +49,6 @@
#include <xen/balloon.h>
#include "common.h"

/*
* These are rather arbitrary. They are fairly large because adjacent requests
* pulled from a communication ring are quite likely to end up being part of
* the same scatter/gather request at the disc.
*
* ** TRY INCREASING 'xen_blkif_reqs' IF WRITE SPEEDS SEEM TOO LOW **
*
* This will increase the chances of being able to write whole tracks.
* 64 should be enough to keep us competitive with Linux.
*/
static int xen_blkif_reqs = 64;
module_param_named(reqs, xen_blkif_reqs, int, 0);
MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate");

/*
* Maximum number of unused free pages to keep in the internal buffer.
* Setting this to a value too low will reduce memory used in each backend,
Expand Down Expand Up @@ -112,53 +98,11 @@ MODULE_PARM_DESC(max_persistent_grants,
static unsigned int log_stats;
module_param(log_stats, int, 0644);

/*
* Each outstanding request that we've passed to the lower device layers has a
* 'pending_req' allocated to it. Each buffer_head that completes decrements
* the pendcnt towards zero. When it hits zero, the specified domain has a
* response queued for it, with the saved 'id' passed back.
*/
struct pending_req {
struct xen_blkif *blkif;
u64 id;
int nr_pages;
atomic_t pendcnt;
unsigned short operation;
int status;
struct list_head free_list;
struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct persistent_gnt *persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
grant_handle_t grant_handles[BLKIF_MAX_SEGMENTS_PER_REQUEST];
};

#define BLKBACK_INVALID_HANDLE (~0)

/* Number of free pages to remove on each call to free_xenballooned_pages */
#define NUM_BATCH_FREE_PAGES 10

struct xen_blkbk {
struct pending_req *pending_reqs;
/* List of all 'pending_req' available */
struct list_head pending_free;
/* And its spinlock. */
spinlock_t pending_free_lock;
wait_queue_head_t pending_free_wq;
};

static struct xen_blkbk *blkbk;

/*
* Little helpful macro to figure out the index and virtual address of the
* pending_pages[..]. For each 'pending_req' we have have up to
* BLKIF_MAX_SEGMENTS_PER_REQUEST (11) pages. The seg would be from 0 through
* 10 and would index in the pending_pages[..].
*/
static inline int vaddr_pagenr(struct pending_req *req, int seg)
{
return (req - blkbk->pending_reqs) *
BLKIF_MAX_SEGMENTS_PER_REQUEST + seg;
}

static inline int get_free_page(struct xen_blkif *blkif, struct page **page)
{
unsigned long flags;
Expand Down Expand Up @@ -485,36 +429,36 @@ static void purge_persistent_gnt(struct xen_blkif *blkif)
/*
* Retrieve from the 'pending_reqs' a free pending_req structure to be used.
*/
static struct pending_req *alloc_req(void)
static struct pending_req *alloc_req(struct xen_blkif *blkif)
{
struct pending_req *req = NULL;
unsigned long flags;

spin_lock_irqsave(&blkbk->pending_free_lock, flags);
if (!list_empty(&blkbk->pending_free)) {
req = list_entry(blkbk->pending_free.next, struct pending_req,
spin_lock_irqsave(&blkif->pending_free_lock, flags);
if (!list_empty(&blkif->pending_free)) {
req = list_entry(blkif->pending_free.next, struct pending_req,
free_list);
list_del(&req->free_list);
}
spin_unlock_irqrestore(&blkbk->pending_free_lock, flags);
spin_unlock_irqrestore(&blkif->pending_free_lock, flags);
return req;
}

/*
* Return the 'pending_req' structure back to the freepool. We also
* wake up the thread if it was waiting for a free page.
*/
static void free_req(struct pending_req *req)
static void free_req(struct xen_blkif *blkif, struct pending_req *req)
{
unsigned long flags;
int was_empty;

spin_lock_irqsave(&blkbk->pending_free_lock, flags);
was_empty = list_empty(&blkbk->pending_free);
list_add(&req->free_list, &blkbk->pending_free);
spin_unlock_irqrestore(&blkbk->pending_free_lock, flags);
spin_lock_irqsave(&blkif->pending_free_lock, flags);
was_empty = list_empty(&blkif->pending_free);
list_add(&req->free_list, &blkif->pending_free);
spin_unlock_irqrestore(&blkif->pending_free_lock, flags);
if (was_empty)
wake_up(&blkbk->pending_free_wq);
wake_up(&blkif->pending_free_wq);
}

/*
Expand Down Expand Up @@ -649,8 +593,8 @@ int xen_blkif_schedule(void *arg)
if (timeout == 0)
goto purge_gnt_list;
timeout = wait_event_interruptible_timeout(
blkbk->pending_free_wq,
!list_empty(&blkbk->pending_free) ||
blkif->pending_free_wq,
!list_empty(&blkif->pending_free) ||
kthread_should_stop(),
timeout);
if (timeout == 0)
Expand Down Expand Up @@ -907,7 +851,7 @@ static int dispatch_other_io(struct xen_blkif *blkif,
struct blkif_request *req,
struct pending_req *pending_req)
{
free_req(pending_req);
free_req(blkif, pending_req);
make_response(blkif, req->u.other.id, req->operation,
BLKIF_RSP_EOPNOTSUPP);
return -EIO;
Expand Down Expand Up @@ -967,7 +911,7 @@ static void __end_block_io_op(struct pending_req *pending_req, int error)
if (atomic_read(&pending_req->blkif->drain))
complete(&pending_req->blkif->drain_complete);
}
free_req(pending_req);
free_req(pending_req->blkif, pending_req);
}
}

Expand Down Expand Up @@ -1010,7 +954,7 @@ __do_block_io_op(struct xen_blkif *blkif)
break;
}

pending_req = alloc_req();
pending_req = alloc_req(blkif);
if (NULL == pending_req) {
blkif->st_oo_req++;
more_to_do = 1;
Expand Down Expand Up @@ -1044,7 +988,7 @@ __do_block_io_op(struct xen_blkif *blkif)
goto done;
break;
case BLKIF_OP_DISCARD:
free_req(pending_req);
free_req(blkif, pending_req);
if (dispatch_discard_io(blkif, &req))
goto done;
break;
Expand Down Expand Up @@ -1246,7 +1190,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
fail_response:
/* Haven't submitted any bio's yet. */
make_response(blkif, req->u.rw.id, req->operation, BLKIF_RSP_ERROR);
free_req(pending_req);
free_req(blkif, pending_req);
msleep(1); /* back off a bit */
return -EIO;

Expand Down Expand Up @@ -1303,51 +1247,20 @@ static void make_response(struct xen_blkif *blkif, u64 id,

static int __init xen_blkif_init(void)
{
int i;
int rc = 0;

if (!xen_domain())
return -ENODEV;

blkbk = kzalloc(sizeof(struct xen_blkbk), GFP_KERNEL);
if (!blkbk) {
pr_alert(DRV_PFX "%s: out of memory!\n", __func__);
return -ENOMEM;
}


blkbk->pending_reqs = kzalloc(sizeof(blkbk->pending_reqs[0]) *
xen_blkif_reqs, GFP_KERNEL);

if (!blkbk->pending_reqs) {
rc = -ENOMEM;
goto out_of_memory;
}

rc = xen_blkif_interface_init();
if (rc)
goto failed_init;

INIT_LIST_HEAD(&blkbk->pending_free);
spin_lock_init(&blkbk->pending_free_lock);
init_waitqueue_head(&blkbk->pending_free_wq);

for (i = 0; i < xen_blkif_reqs; i++)
list_add_tail(&blkbk->pending_reqs[i].free_list,
&blkbk->pending_free);

rc = xen_blkif_xenbus_init();
if (rc)
goto failed_init;

return 0;

out_of_memory:
pr_alert(DRV_PFX "%s: out of memory\n", __func__);
failed_init:
kfree(blkbk->pending_reqs);
kfree(blkbk);
blkbk = NULL;
return rc;
}

Expand Down
30 changes: 30 additions & 0 deletions drivers/block/xen-blkback/common.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,9 @@ struct backend_info;
*/
#define PERSISTENT_GNT_WAS_ACTIVE 1

/* Number of requests that we can fit in a ring */
#define XEN_BLKIF_REQS 32

struct persistent_gnt {
struct page *page;
grant_ref_t gnt;
Expand Down Expand Up @@ -242,6 +245,14 @@ struct xen_blkif {
int free_pages_num;
struct list_head free_pages;

/* Allocation of pending_reqs */
struct pending_req *pending_reqs;
/* List of all 'pending_req' available */
struct list_head pending_free;
/* And its spinlock. */
spinlock_t pending_free_lock;
wait_queue_head_t pending_free_wq;

/* statistics */
unsigned long st_print;
unsigned long long st_rd_req;
Expand All @@ -255,6 +266,25 @@ struct xen_blkif {
wait_queue_head_t waiting_to_free;
};

/*
* Each outstanding request that we've passed to the lower device layers has a
* 'pending_req' allocated to it. Each buffer_head that completes decrements
* the pendcnt towards zero. When it hits zero, the specified domain has a
* response queued for it, with the saved 'id' passed back.
*/
struct pending_req {
struct xen_blkif *blkif;
u64 id;
int nr_pages;
atomic_t pendcnt;
unsigned short operation;
int status;
struct list_head free_list;
struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct persistent_gnt *persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
grant_handle_t grant_handles[BLKIF_MAX_SEGMENTS_PER_REQUEST];
};


#define vbd_sz(_v) ((_v)->bdev->bd_part ? \
(_v)->bdev->bd_part->nr_sects : \
Expand Down
26 changes: 26 additions & 0 deletions drivers/block/xen-blkback/xenbus.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -105,6 +105,7 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
static struct xen_blkif *xen_blkif_alloc(domid_t domid)
{
struct xen_blkif *blkif;
int i;

blkif = kmem_cache_zalloc(xen_blkif_cachep, GFP_KERNEL);
if (!blkif)
Expand All @@ -124,6 +125,21 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
blkif->free_pages_num = 0;
atomic_set(&blkif->persistent_gnt_in_use, 0);

blkif->pending_reqs = kcalloc(XEN_BLKIF_REQS,
sizeof(blkif->pending_reqs[0]),
GFP_KERNEL);
if (!blkif->pending_reqs) {
kmem_cache_free(xen_blkif_cachep, blkif);
return ERR_PTR(-ENOMEM);
}
INIT_LIST_HEAD(&blkif->pending_free);
spin_lock_init(&blkif->pending_free_lock);
init_waitqueue_head(&blkif->pending_free_wq);

for (i = 0; i < XEN_BLKIF_REQS; i++)
list_add_tail(&blkif->pending_reqs[i].free_list,
&blkif->pending_free);

return blkif;
}

Expand Down Expand Up @@ -203,8 +219,18 @@ static void xen_blkif_disconnect(struct xen_blkif *blkif)

static void xen_blkif_free(struct xen_blkif *blkif)
{
struct pending_req *req;
int i = 0;

if (!atomic_dec_and_test(&blkif->refcnt))
BUG();

/* Check that there is no request in use */
list_for_each_entry(req, &blkif->pending_free, free_list)
i++;
BUG_ON(i != XEN_BLKIF_REQS);

kfree(blkif->pending_reqs);
kmem_cache_free(xen_blkif_cachep, blkif);
}

Expand Down

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