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    SubjectRe: queue_nr_requests needs to be selective


    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.

    :-)

    Thanks for the help.

    Jeff


    On Fri, Mar 01, 2002 at 04:49:47PM -0800, Andrew Morton wrote:
    > "Jeff V. Merkey" wrote:
    > >
    > > ...
    > > > OK. So would it suffice to make queue_nr_requests an argument to
    > > > a new blk_init_queue()?
    > > >
    > > > - blk_init_queue(q, sci_request);
    > > > + blk_init_queue_ng(q, sci_request, 1024);
    > > >
    > >
    > > Andrew,
    > >
    > > Yep. This will do it.
    >
    > OK. The requirement seems eminently sensible to me. Could
    > you please verify the suitability of this patch? And if Jens
    > is OK with it, I'll stick it in the pile marked "Brazil".
    >
    >
    > --- 2.4.19-pre2/drivers/block/ll_rw_blk.c~blk-queue Fri Mar 1 15:30:13 2002
    > +++ 2.4.19-pre2-akpm/drivers/block/ll_rw_blk.c Fri Mar 1 15:57:07 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]);
    > @@ -330,9 +320,11 @@ void generic_unplug_device(void *data)
    > spin_unlock_irqrestore(&io_request_lock, flags);
    > }
    >
    > -static void blk_init_free_list(request_queue_t *q)
    > +static void blk_init_free_list(request_queue_t *q, int nr_requests)
    > {
    > struct request *rq;
    > + struct sysinfo si;
    > + int megs; /* Total memory, in megabytes */
    > int i;
    >
    > INIT_LIST_HEAD(&q->rq[READ].free);
    > @@ -340,10 +332,17 @@ static void blk_init_free_list(request_q
    > q->rq[READ].count = 0;
    > q->rq[WRITE].count = 0;
    >
    > + si_meminfo(&si);
    > + megs = si.totalram >> (20 - PAGE_SHIFT);
    > + q->nr_requests = nr_requests;
    > + if (megs < 32)
    > + q->nr_requests /= 2;
    > + q->batch_requests = q->nr_requests / 4;
    > +
    > /*
    > * Divide requests in half between read and write
    > */
    > - for (i = 0; i < queue_nr_requests; i++) {
    > + for (i = 0; i < 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 */
    > @@ -364,15 +363,17 @@ static void blk_init_free_list(request_q
    > static int __make_request(request_queue_t * q, int rw, struct buffer_head * bh);
    >
    > /**
    > - * blk_init_queue - prepare a request queue for use with a block device
    > + * __blk_init_queue - prepare a request queue for use with a block device
    > * @q: The &request_queue_t to be initialised
    > * @rfn: The function to be called to process requests that have been
    > * placed on the queue.
    > + * @nr_requests: the number of request structures on each of the device's
    > + * read and write request lists.
    > *
    > * Description:
    > * If a block device wishes to use the standard request handling procedures,
    > * which sorts requests and coalesces adjacent requests, then it must
    > - * call blk_init_queue(). The function @rfn will be called when there
    > + * call __blk_init_queue(). The function @rfn will be called when there
    > * are requests on the queue that need to be processed. If the device
    > * supports plugging, then @rfn may not be called immediately when requests
    > * are available on the queue, but may be called at some time later instead.
    > @@ -392,15 +393,21 @@ static int __make_request(request_queue_
    > * whenever the given queue is unplugged. This behaviour can be changed with
    > * blk_queue_headactive().
    > *
    > + * Your selected value of nr_requests will be scaled down for small
    > + * machines. See blk_init_free_list().
    > + *
    > + * If nr_requests is less than 16, things will probably fail mysteriously.
    > + *
    > * Note:
    > - * blk_init_queue() must be paired with a blk_cleanup_queue() call
    > + * __blk_init_queue() must be paired with a blk_cleanup_queue() call
    > * when the block device is deactivated (such as at module unload).
    > **/
    > -void blk_init_queue(request_queue_t * q, request_fn_proc * rfn)
    > +void __blk_init_queue(request_queue_t * q,
    > + request_fn_proc * rfn, int nr_requests)
    > {
    > INIT_LIST_HEAD(&q->queue_head);
    > elevator_init(&q->elevator, ELEVATOR_LINUS);
    > - blk_init_free_list(q);
    > + blk_init_free_list(q, nr_requests);
    > q->request_fn = rfn;
    > q->back_merge_fn = ll_back_merge_fn;
    > q->front_merge_fn = ll_front_merge_fn;
    > @@ -610,7 +617,7 @@ 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 +809,7 @@ 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 +1156,9 @@ 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 +1174,6 @@ 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
    > @@ -1296,7 +1284,7 @@ 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_init_queue);
    > +EXPORT_SYMBOL(__blk_init_queue);
    > EXPORT_SYMBOL(blk_get_queue);
    > EXPORT_SYMBOL(blk_cleanup_queue);
    > EXPORT_SYMBOL(blk_queue_headactive);
    > --- 2.4.19-pre2/include/linux/blkdev.h~blk-queue Fri Mar 1 15:31:09 2002
    > +++ 2.4.19-pre2-akpm/include/linux/blkdev.h Fri Mar 1 15:41:50 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;
    > @@ -157,7 +167,8 @@ extern void blkdev_release_request(struc
    > /*
    > * Access functions for manipulating queue properties
    > */
    > -extern void blk_init_queue(request_queue_t *, request_fn_proc *);
    > +#define blk_init_queue(q, fn) __blk_init_queue(q, fn, 128)
    > +extern void __blk_init_queue(request_queue_t *, request_fn_proc *, int);
    > extern void blk_cleanup_queue(request_queue_t *);
    > extern void blk_queue_headactive(request_queue_t *, int);
    > extern void blk_queue_make_request(request_queue_t *, make_request_fn *);
    >
    >
    > -
    > -
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