diff options
Diffstat (limited to 'block/iscsi.c')
| -rw-r--r-- | block/iscsi.c | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/block/iscsi.c b/block/iscsi.c index 6b8a0a34f7..e8d26bb781 100644 --- a/block/iscsi.c +++ b/block/iscsi.c @@ -95,7 +95,15 @@ typedef struct IscsiAIOCB { #define NOP_INTERVAL 5000 #define MAX_NOP_FAILURES 3 #define ISCSI_CMD_RETRIES 5 -#define ISCSI_CHECKALLOC_THRES 63 + +/* this threshhold is a trade-off knob to choose between + * the potential additional overhead of an extra GET_LBA_STATUS request + * vs. unnecessarily reading a lot of zero sectors over the wire. + * If a read request is greater or equal than ISCSI_CHECKALLOC_THRES + * sectors we check the allocation status of the area covered by the + * request first if the allocationmap indicates that the area might be + * unallocated. */ +#define ISCSI_CHECKALLOC_THRES 64 static void iscsi_bh_cb(void *p) @@ -505,7 +513,7 @@ static int coroutine_fn iscsi_co_readv(BlockDriverState *bs, } #if defined(LIBISCSI_FEATURE_IOVECTOR) - if (iscsilun->lbprz && nb_sectors > ISCSI_CHECKALLOC_THRES && + if (iscsilun->lbprz && nb_sectors >= ISCSI_CHECKALLOC_THRES && !iscsi_allocationmap_is_allocated(iscsilun, sector_num, nb_sectors)) { int64_t ret; int pnum; |