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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v1 5/7] xen-blkback: make the queue of free requests per backend
On Wed, Mar 27, 2013 at 12:10:41PM +0100, Roger Pau Monne wrote:
> 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@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxx
> ---
> Changes since RFC:
> * Replace kzalloc with kcalloc.
> ---
> drivers/block/xen-blkback/blkback.c | 125
> +++++++----------------------------
> drivers/block/xen-blkback/common.h | 27 ++++++++
> drivers/block/xen-blkback/xenbus.c | 19 +++++
> 3 files changed, 70 insertions(+), 101 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/blkback.c
> b/drivers/block/xen-blkback/blkback.c
> index e6542d5..a1c9dad 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.
You might want to clarify that 'Any value less than that is sure to
cause problems.'
At which point perhaps we should have some logic to enforce that?
> */
> -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");
Do we even need this anymore? I mean if the optimial size is 32 and going
below that is silly. Going above that is silly as well - as we won't be using
the extra count.
Can we just rip this module parameter out?
>
> /*
> * Maximum number of unused free pages to keep in the internal buffer.
> @@ -120,53 +116,11 @@ MODULE_PARM_DESC(lru_percent_clean,
> 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;
> @@ -471,18 +425,18 @@ 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;
> }
>
> @@ -490,17 +444,17 @@ 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);
> }
>
> /*
> @@ -635,8 +589,8 @@ 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)
> @@ -883,7 +837,7 @@ 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;
> @@ -943,7 +897,7 @@ 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);
> }
> }
>
> @@ -986,7 +940,7 @@ __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;
> @@ -1020,7 +974,7 @@ __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;
> @@ -1222,7 +1176,7 @@ 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;
>
> @@ -1279,51 +1233,20 @@ 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 f43782c..debff44 100644
> --- a/drivers/block/xen-blkback/common.h
> +++ b/drivers/block/xen-blkback/common.h
> @@ -236,6 +236,14 @@ 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;
> @@ -249,6 +257,25 @@ 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 : \
> diff --git a/drivers/block/xen-blkback/xenbus.c
> b/drivers/block/xen-blkback/xenbus.c
> index e0fd92a..bf7344f 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;
How about just sticking it in 'common.h'?
> +
> static struct kmem_cache *xen_blkif_cachep;
> static void connect(struct backend_info *);
> static int connect_ring(struct backend_info *);
> @@ -105,6 +107,7 @@ 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)
> @@ -124,6 +127,21 @@ 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;
> }
>
> @@ -205,6 +223,7 @@ static void xen_blkif_free(struct xen_blkif *blkif)
> {
> if (!atomic_dec_and_test(&blkif->refcnt))
> BUG();
For sanity, should we have something like this:
struct pending_req *p;
i = 0;
list_for_each_entry (p, &blkif->pending_free, free_list)
i++;
BUG_ON(i != xen_blkif_reqs);
As that would mean somebody did not call 'free_req' and we have a loose one
laying
around.
Or perhaps just leak the offending struct and then don't do 'kfree'?
> + kfree(blkif->pending_reqs);
> kmem_cache_free(xen_blkif_cachep, blkif);
> }
>
> --
> 1.7.7.5 (Apple Git-26)
>
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