On Sat, Oct 25, 2014 at 06:55:50PM +0200, Peter Lieven wrote:
> diff --git a/block.c b/block.c
> index f05ea0c..f3da5dd 100644
> --- a/block.c
> +++ b/block.c
> @@ -884,6 +884,10 @@ static QemuOptsList bdrv_runtime_opts = {
> .name = "node-name",
> .type = QEMU_OPT_STRING,
> .help = "Node name of the block device node",
> + },{
> + .name = "write-merging",
> + .type = QEMU_OPT_BOOL,
> + .help = "enable write merging (default: true)",
QEMU_OPT_BOOL takes "on"/"off" instead of "true"/"false":
s/true/on/
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 2095f9e..74d1960 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -214,6 +214,8 @@
> #
> # @detect_zeroes: detect and optimize zero writes (Since 2.1)
> #
> +# @write_merging: true if write merging is enabled (Since 2.2)
> +#
> # @bps: total throughput limit in bytes per second is specified
> #
> # @bps_rd: read throughput limit in bytes per second is specified
> @@ -250,6 +252,7 @@
> '*backing_file': 'str', 'backing_file_depth': 'int',
> 'encrypted': 'bool', 'encryption_key_missing': 'bool',
> 'detect_zeroes': 'BlockdevDetectZeroesOptions',
> + 'write_merging': 'bool',
> 'bps': 'int', 'bps_rd': 'int', 'bps_wr': 'int',
> 'iops': 'int', 'iops_rd': 'int', 'iops_wr': 'int',
> 'image': 'ImageInfo',
> @@ -1185,6 +1188,10 @@
> # (default: false)
> # @detect-zeroes: #optional detect and optimize zero writes (Since 2.1)
> # (default: off)
> +# @write-merging: #optional enable the merging of write requests
> +# also known as multiwrite_merge (Since 2.2)
> +# (default: true, but this might change in the future
> +# depending on format/protocol/features used)
> #
> # Since: 1.7
> ##
> @@ -1198,7 +1205,8 @@
> '*rerror': 'BlockdevOnError',
> '*werror': 'BlockdevOnError',
> '*read-only': 'bool',
> - '*detect-zeroes': 'BlockdevDetectZeroesOptions' } }
> + '*detect-zeroes': 'BlockdevDetectZeroesOptions',
> + '*write-merging': 'bool' } }
>
> ##
> # @BlockdevOptionsFile
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 22cf3b9..d2f756f 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -432,6 +432,7 @@ DEF("drive", HAS_ARG, QEMU_OPTION_drive,
> "
> [,werror=ignore|stop|report|enospc][,id=name][,aio=threads|native]\n"
> " [,readonly=on|off][,copy-on-read=on|off]\n"
> " [,discard=ignore|unmap][,detect-zeroes=on|off|unmap]\n"
> + " [,write-merging=on|off]\n"
> " [[,bps=b]|[[,bps_rd=r][,bps_wr=w]]]\n"
> " [[,iops=i]|[[,iops_rd=r][,iops_wr=w]]]\n"
> " [[,bps_max=bm]|[[,bps_rd_max=rm][,bps_wr_max=wm]]]\n"
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index 1abd619..2c20207 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -2104,6 +2104,7 @@ Each json-object contain the following:
> - "iops_size": I/O size when limiting by iops (json-int)
> - "detect_zeroes": detect and optimize zero writing (json-string)
> - Possible values: "off", "on", "unmap"
> + - "write_merging": enable merging of write requests (json-bool)
> - "image": the detail of the image, it is a json-object containing
> the following:
> - "filename": image file name (json-string)
> @@ -2181,6 +2182,7 @@ Example:
> "iops_wr_max": 0,
> "iops_size": 0,
> "detect_zeroes": "on",
> + "write_merging": "true",
> "image":{
> "filename":"disks/test.qcow2",
> "format":"qcow2",
The big question is whether these user-visible interfaces make sense if
write merging will be moved from block.c into virtio-blk.c in the
future. Once an interface has been added it cannot be removed.
I think write merging in block.c is fine since other emulated storage
controllers like virtio-scsi might also choose to use it.
But I want to raise the point for discussion in case others have strong
feelings.
Stefan
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