From c47206e25f28232ff979994c32758c82841d81cd Mon Sep 17 00:00:00 2001 From: Roger Pau Monne Date: Mon, 12 Aug 2013 12:53:43 +0200 Subject: xen-blkfront: improve aproximation of required grants per request MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Improve the calculation of required grants to process a request by using nr_phys_segments instead of always assuming a request is going to use all posible segments. nr_phys_segments contains the number of scatter-gather DMA addr+len pairs, which is basically what we put at every granted page. for_each_sg iterates over the DMA addr+len pairs and uses a grant page for each of them. Signed-off-by: Roger Pau Monné Reviewed-by: David Vrabel Cc: Konrad Rzeszutek Wilk Cc: David Vrabel Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Jens Axboe --- drivers/block/xen-blkfront.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) (limited to 'drivers/block') diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index 429d52640940..5b8a15483a4c 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -400,10 +400,13 @@ static int blkif_queue_request(struct request *req) if (unlikely(info->connected != BLKIF_STATE_CONNECTED)) return 1; - max_grefs = info->max_indirect_segments ? - info->max_indirect_segments + - INDIRECT_GREFS(info->max_indirect_segments) : - BLKIF_MAX_SEGMENTS_PER_REQUEST; + max_grefs = req->nr_phys_segments; + if (max_grefs > BLKIF_MAX_SEGMENTS_PER_REQUEST) + /* + * If we are using indirect segments we need to account + * for the indirect grefs used in the request. + */ + max_grefs += INDIRECT_GREFS(req->nr_phys_segments); /* Check if we have enough grants to allocate a requests */ if (info->persistent_gnts_c < max_grefs) { -- cgit v1.2.3