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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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