Nowaday SCSI drivers in guests are able to alight UNMAP requests before
sending to the device. Right now QEMU provides an ability to set
this via "discard_granularity" property of the block device which could
be used by management layer.
Though, in particular, from the point of QEMU, there is
pdiscard_granularity on the format driver level, f.e. on QCOW2 or iSCSI.
It would be beneficial to pass this value as a default for this
property.
Technically this should reduce the amount of useless UNMAP requests
from the guest to the host.
Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Kevin Wolf <kw...@redhat.com>
CC: Max Reitz <mre...@redhat.com>
CC: Paolo Bonzini <pbonz...@redhat.com>
CC: Fam Zheng <f...@euphon.net>
---
block/block-backend.c | 13 +++++++++++++
hw/scsi/scsi-disk.c | 4 ++--
include/sysemu/block-backend.h | 1 +
3 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/block/block-backend.c b/block/block-backend.c
index f6ea824308..17a709a551 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -21,11 +21,13 @@
#include "qapi/qapi-events-block.h"
#include "qemu/id.h"
#include "qemu/option.h"
+#include "qemu/units.h"
#include "trace.h"
#include "migration/misc.h"
/* Number of coroutines to reserve per attached device model */
#define COROUTINE_POOL_RESERVATION 64
+#define DEFAULT_DISCARD_GRANULARITY (4 * KiB)
#define NOT_DONE 0x7fffffff /* used while emulated sync operation in progress
*/
@@ -2042,6 +2044,17 @@ int blk_probe_geometry(BlockBackend *blk, HDGeometry
*geo)
return bdrv_probe_geometry(blk_bs(blk), geo);
}
+int blk_discard_granularity(BlockBackend *blk)
+{
+ BlockDriverState *bs = blk_bs(blk);
+
+ if (bs == NULL) {
+ return DEFAULT_DISCARD_GRANULARITY;
+ }
+
+ return bs->bl.pdiscard_alignment;
+}
+
/*
* Updates the BlockBackendRootState object with data from the currently
* attached BlockDriverState.
diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index d4e83aef0e..f0ff099114 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -43,7 +43,6 @@
#define SCSI_MAX_INQUIRY_LEN 256
#define SCSI_MAX_MODE_LEN 256
-#define DEFAULT_DISCARD_GRANULARITY (4 * KiB)
#define DEFAULT_MAX_UNMAP_SIZE (1 * GiB)
#define DEFAULT_MAX_IO_SIZE INT_MAX /* 2 GB - 1 block */
@@ -2338,7 +2337,8 @@ static void scsi_realize(SCSIDevice *dev, Error **errp)
if (s->qdev.conf.discard_granularity == -1) {
s->qdev.conf.discard_granularity =
- MAX(s->qdev.conf.logical_block_size, DEFAULT_DISCARD_GRANULARITY);
+ MAX(s->qdev.conf.logical_block_size,
+ blk_discard_granularity(s->qdev.conf.blk));
}
if (!s->version) {
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 832a4bf168..18428e685d 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -218,6 +218,7 @@ int blk_save_vmstate(BlockBackend *blk, const uint8_t *buf,
int blk_load_vmstate(BlockBackend *blk, uint8_t *buf, int64_t pos, int size);
int blk_probe_blocksizes(BlockBackend *blk, BlockSizes *bsz);
int blk_probe_geometry(BlockBackend *blk, HDGeometry *geo);
+int blk_discard_granularity(BlockBackend *blk);
BlockAIOCB *blk_abort_aio_request(BlockBackend *blk,
BlockCompletionFunc *cb,
void *opaque, int ret);
--
2.17.1
