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block/iscsi: clarify the meaning of ISCSI_CHECKALLOC_THRES 

Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Peter Lieven 2014-04-28 17:11:33 +02:00 committed by Paolo Bonzini
parent b03c38057b
commit 5917af812e
1 changed files with 10 additions and 2 deletions
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12
block/iscsi.c
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@ -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;