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    SubjectRe: queue_nr_requests needs to be selective
    "Jeff V. Merkey" wrote:
    >
    > Andrew,
    >
    > Patch tested and stable. I has to manually modify the value
    > in /usr/src/linux/include/linux/blkdev.h from 128 to 1024
    > since I noticed the 3Ware driver is going through the scsi.c
    > call to blk_init_queue() macro in this include file. I am
    > assuming that at some point, Adam and the other folks will
    > call this api directly.
    >
    > Performance increased 2-3 % to 319 MB/S on dual 33/66 buses,
    > and utilization dropped to 27% +-. All of this activity is
    > DMA based and copyless between reading/writing nodes and
    > I am running this UP and getting these numbers. I ran SMP
    > as well and it also looks good.
    >
    > Someone needs to look at just how the drivers will call
    > __blk_init_queue() directly to setup custom depth queues
    > from scsi.c since this call is originating there for
    > those IDE RAID drivers that fake out the system in thinking
    > they are SCSI.
    >

    So it would be more straightforward to just allow the queue
    to be grown later on?



    --- 2.4.19-pre2/drivers/block/ll_rw_blk.c~blk-queue Fri Mar 1 19:40:12 2002
    +++ 2.4.19-pre2-akpm/drivers/block/ll_rw_blk.c Fri Mar 1 19:48:33 2002
    @@ -117,16 +117,6 @@ int * max_readahead[MAX_BLKDEV];
    */
    int * max_sectors[MAX_BLKDEV];

    -/*
    - * The total number of requests in each queue.
    - */
    -static int queue_nr_requests;
    -
    -/*
    - * The threshold around which we make wakeup decisions
    - */
    -static int batch_requests;
    -
    static inline int get_max_sectors(kdev_t dev)
    {
    if (!max_sectors[MAJOR(dev)])
    @@ -180,7 +170,7 @@ static int __blk_cleanup_queue(struct re
    **/
    void blk_cleanup_queue(request_queue_t * q)
    {
    - int count = queue_nr_requests;
    + int count = q->nr_requests;

    count -= __blk_cleanup_queue(&q->rq[READ]);
    count -= __blk_cleanup_queue(&q->rq[WRITE]);
    @@ -330,31 +320,62 @@ void generic_unplug_device(void *data)
    spin_unlock_irqrestore(&io_request_lock, flags);
    }

    +/** blk_grow_request_list
    + * @q: The &request_queue_t
    + * @nr_requests: how many requests are desired
    + *
    + * More free requests are added to the queue's free lists, bringing
    + * the total number of requests to @nr_requests.
    + *
    + * The requests are added equally to the request queue's read
    + * and write freelists.
    + *
    + * This function can sleep.
    + *
    + * Returns the (new) number of requests which the queue has available.
    + */
    +int blk_grow_request_list(request_queue_t *q, int nr_requests)
    +{
    + spin_lock_irq(&io_request_lock);
    + while (q->nr_requests < nr_requests) {
    + struct request *rq;
    + int rw;
    +
    + spin_unlock_irq(&io_request_lock);
    + rq = kmem_cache_alloc(request_cachep, SLAB_KERNEL);
    + spin_lock_irq(&io_request_lock);
    + if (rq == NULL)
    + break;
    + memset(rq, 0, sizeof(*rq));
    + rq->rq_status = RQ_INACTIVE;
    + rw = q->nr_requests & 1;
    + list_add(&rq->queue, &q->rq[rw].free);
    + q->rq[rw].count++;
    + q->nr_requests++;
    + }
    + q->batch_requests = q->nr_requests / 4;
    + spin_unlock_irq(&io_request_lock);
    + return q->nr_requests;
    +}
    +
    static void blk_init_free_list(request_queue_t *q)
    {
    - struct request *rq;
    - int i;
    + struct sysinfo si;
    + int megs; /* Total memory, in megabytes */
    + int nr_requests;

    INIT_LIST_HEAD(&q->rq[READ].free);
    INIT_LIST_HEAD(&q->rq[WRITE].free);
    q->rq[READ].count = 0;
    q->rq[WRITE].count = 0;
    + q->nr_requests = 0;

    - /*
    - * Divide requests in half between read and write
    - */
    - for (i = 0; i < queue_nr_requests; i++) {
    - rq = kmem_cache_alloc(request_cachep, SLAB_KERNEL);
    - if (rq == NULL) {
    - /* We'll get a `leaked requests' message from blk_cleanup_queue */
    - printk(KERN_EMERG "blk_init_free_list: error allocating requests\n");
    - break;
    - }
    - memset(rq, 0, sizeof(struct request));
    - rq->rq_status = RQ_INACTIVE;
    - list_add(&rq->queue, &q->rq[i&1].free);
    - q->rq[i&1].count++;
    - }
    + si_meminfo(&si);
    + megs = si.totalram >> (20 - PAGE_SHIFT);
    + nr_requests = 128;
    + if (megs < 32)
    + nr_requests /= 2;
    + blk_grow_request_list(q, nr_requests);

    init_waitqueue_head(&q->wait_for_requests[0]);
    init_waitqueue_head(&q->wait_for_requests[1]);
    @@ -610,7 +631,7 @@ void blkdev_release_request(struct reque
    */
    if (q) {
    list_add(&req->queue, &q->rq[rw].free);
    - if (++q->rq[rw].count >= batch_requests &&
    + if (++q->rq[rw].count >= q->batch_requests &&
    waitqueue_active(&q->wait_for_requests[rw]))
    wake_up(&q->wait_for_requests[rw]);
    }
    @@ -802,7 +823,7 @@ get_rq:
    * See description above __get_request_wait()
    */
    if (rw_ahead) {
    - if (q->rq[rw].count < batch_requests) {
    + if (q->rq[rw].count < q->batch_requests) {
    spin_unlock_irq(&io_request_lock);
    goto end_io;
    }
    @@ -1149,12 +1170,9 @@ void end_that_request_last(struct reques
    blkdev_release_request(req);
    }

    -#define MB(kb) ((kb) << 10)
    -
    int __init blk_dev_init(void)
    {
    struct blk_dev_struct *dev;
    - int total_ram;

    request_cachep = kmem_cache_create("blkdev_requests",
    sizeof(struct request),
    @@ -1170,22 +1188,6 @@ int __init blk_dev_init(void)
    memset(max_readahead, 0, sizeof(max_readahead));
    memset(max_sectors, 0, sizeof(max_sectors));

    - total_ram = nr_free_pages() << (PAGE_SHIFT - 10);
    -
    - /*
    - * Free request slots per queue.
    - * (Half for reads, half for writes)
    - */
    - queue_nr_requests = 64;
    - if (total_ram > MB(32))
    - queue_nr_requests = 128;
    -
    - /*
    - * Batch frees according to queue length
    - */
    - batch_requests = queue_nr_requests/4;
    - printk("block: %d slots per queue, batch=%d\n", queue_nr_requests, batch_requests);
    -
    #ifdef CONFIG_AMIGA_Z2RAM
    z2_init();
    #endif
    @@ -1296,6 +1298,7 @@ int __init blk_dev_init(void)
    EXPORT_SYMBOL(io_request_lock);
    EXPORT_SYMBOL(end_that_request_first);
    EXPORT_SYMBOL(end_that_request_last);
    +EXPORT_SYMBOL(blk_grow_request_list);
    EXPORT_SYMBOL(blk_init_queue);
    EXPORT_SYMBOL(blk_get_queue);
    EXPORT_SYMBOL(blk_cleanup_queue);
    --- 2.4.19-pre2/include/linux/blkdev.h~blk-queue Fri Mar 1 19:40:12 2002
    +++ 2.4.19-pre2-akpm/include/linux/blkdev.h Fri Mar 1 19:40:12 2002
    @@ -79,6 +79,16 @@ struct request_queue
    struct request_list rq[2];

    /*
    + * The total number of requests on each queue
    + */
    + int nr_requests;
    +
    + /*
    + * Batching threshold for sleep/wakeup decisions
    + */
    + int batch_requests;
    +
    + /*
    * Together with queue_head for cacheline sharing
    */
    struct list_head queue_head;
    @@ -157,6 +167,7 @@ extern void blkdev_release_request(struc
    /*
    * Access functions for manipulating queue properties
    */
    +extern int blk_grow_request_list(request_queue_t *q, int nr_requests);
    extern void blk_init_queue(request_queue_t *, request_fn_proc *);
    extern void blk_cleanup_queue(request_queue_t *);
    extern void blk_queue_headactive(request_queue_t *, int);
    -
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