Roger Pau Monne
2013-Aug-12 10:53 UTC
[PATCH v2 1/2] xen-blkfront: improve aproximation of required grants per request
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 <roger.pau@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
---
drivers/block/xen-blkfront.c | 11 +++++++----
1 files changed, 7 insertions(+), 4 deletions(-)
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 2e1ee34..187a437 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) {
--
1.7.7.5 (Apple Git-26)
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