Messages in this thread Patch in this message | | | From | Roger Pau Monne <> | Subject | [PATCH RFC 10/12] xen-blkback: make the queue of free requests per backend | Date | Thu, 28 Feb 2013 11:28:53 +0100 |
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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 --- drivers/block/xen-blkback/blkback.c | 123 +++++++---------------------------- drivers/block/xen-blkback/common.h | 27 ++++++++ drivers/block/xen-blkback/xenbus.c | 17 +++++ 3 files changed, 67 insertions(+), 100 deletions(-)
diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c index c43de8a..04ad2aa 100644 --- a/drivers/block/xen-blkback/blkback.c +++ b/drivers/block/xen-blkback/blkback.c @@ -50,18 +50,14 @@ #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. + * This is the number of requests that will be pre-allocated for each backend. + * For better performance this is set to RING_SIZE (32), so requests + * in the ring will never have to wait for a free pending_req. */ -static int xen_blkif_reqs = 64; + +int xen_blkif_reqs = 32; module_param_named(reqs, xen_blkif_reqs, int, 0); -MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate"); +MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate per backend"); /* * Maximum number of grants to map persistently in blkback. For maximum @@ -120,50 +116,8 @@ MODULE_PARM_DESC(max_buffer_pages, 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 persistent_gnt *persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST]; - struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST]; - grant_handle_t grant_handles[BLKIF_MAX_SEGMENTS_PER_REQUEST]; -}; - #define BLKBACK_INVALID_HANDLE (~0) -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; @@ -400,18 +354,18 @@ finished: /* * 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; } @@ -419,17 +373,17 @@ static struct pending_req *alloc_req(void) * 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); } /* @@ -564,8 +518,8 @@ 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) @@ -886,7 +840,7 @@ 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); } } @@ -929,7 +883,7 @@ __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; @@ -954,7 +908,7 @@ __do_block_io_op(struct xen_blkif *blkif) /* Apply all sanity checks to /private copy/ of request. */ barrier(); if (unlikely(req.operation == BLKIF_OP_DISCARD)) { - free_req(pending_req); + free_req(blkif, pending_req); if (dispatch_discard_io(blkif, &req)) break; } else if (dispatch_rw_block_io(blkif, &req, pending_req)) @@ -1157,7 +1111,7 @@ 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; @@ -1213,51 +1167,20 @@ 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; } diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index 604bd30..0b0ad3f 100644 --- a/drivers/block/xen-blkback/common.h +++ b/drivers/block/xen-blkback/common.h @@ -214,6 +214,14 @@ 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; int st_rd_req; @@ -227,6 +235,25 @@ 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 persistent_gnt *persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST]; + struct page *pages[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 : \ diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index d7926ec..8f929cb 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -30,6 +30,8 @@ struct backend_info { char *mode; }; +extern int xen_blkif_reqs; + static struct kmem_cache *xen_blkif_cachep; static void connect(struct backend_info *); static int connect_ring(struct backend_info *); @@ -104,6 +106,7 @@ 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) @@ -122,6 +125,19 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid) spin_lock_init(&blkif->free_pages_lock); INIT_LIST_HEAD(&blkif->free_pages); blkif->free_pages_num = 0; + blkif->pending_reqs = kzalloc(sizeof(blkif->pending_reqs[0]) * + xen_blkif_reqs, 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; } @@ -204,6 +220,7 @@ static void xen_blkif_free(struct xen_blkif *blkif) { if (!atomic_dec_and_test(&blkif->refcnt)) BUG(); + kfree(blkif->pending_reqs); kmem_cache_free(xen_blkif_cachep, blkif); } -- 1.7.7.5 (Apple Git-26) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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