diff options
| author | Peter Lieven <pl@kamp.de> | 2014-04-28 17:11:33 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2014-04-29 11:14:41 +0200 |
| commit | 5917af812e9c4bd6500927b26efe8d3e2f267bd0 (patch) | |
| tree | cc4295ae30c40dd3ca8299deef5ca7f09a48774d /block | |
| parent | b03c38057b7ac4ffb60fa98a26dd4c8d5fa9c54c (diff) | |
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>
Diffstat (limited to 'block')
| -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; |