Message ID | 1413815720-29976-4-git-send-email-pl@kamp.de |
---|---|
State | New |
Headers | show |
On 20.10.2014 at 16:35, Peter Lieven wrote: > the block layer silently merges write requests since It's still s/^t/T/ ;-) > commit 40b4f539. This patch adds a knob to disable > this feature as there has been some discussion lately > if multiwrite is a good idea at all and as it falsifies > benchmarks. > > Signed-off-by: Peter Lieven <pl@kamp.de> > --- > block.c | 9 +++++++++ > block/qapi.c | 1 + > hmp.c | 4 ++++ > include/block/block_int.h | 1 + > qapi/block-core.json | 10 +++++++++- > qemu-options.hx | 1 + > qmp-commands.hx | 2 ++ > 7 files changed, 27 insertions(+), 1 deletion(-) > > diff --git a/block.c b/block.c > index 3b4a59a..ffb2b47 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)", > }, > { /* end of list */ } > }, > @@ -985,6 +989,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file, > bs->drv = drv; > bs->opaque = g_malloc0(drv->instance_size); > bs->enable_write_cache = !!(flags & BDRV_O_CACHE_WB); > + bs->write_merging = qemu_opt_get_bool(opts, "write-merging", true); > > /* Open the image, either directly or using a protocol */ > if (drv->bdrv_file_open) { > @@ -4439,6 +4444,10 @@ static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs, > { > int i, outidx; > > + if (!bs->write_merging) { > + return num_reqs; > + } > + > // Sort requests by start sector > qsort(reqs, num_reqs, sizeof(*reqs), &multiwrite_req_compare); > > diff --git a/block/qapi.c b/block/qapi.c > index a0f26e9..5f09967 100644 > --- a/block/qapi.c > +++ b/block/qapi.c > @@ -59,6 +59,7 @@ BlockDeviceInfo *bdrv_block_device_info(BlockDriverState *bs) > > info->backing_file_depth = bdrv_get_backing_file_depth(bs); > info->detect_zeroes = bs->detect_zeroes; > + info->write_merging = bs->write_merging; > > if (bs->io_limits_enabled) { > ThrottleConfig cfg; > diff --git a/hmp.c b/hmp.c > index baaa9e5..5762444 100644 > --- a/hmp.c > +++ b/hmp.c > @@ -348,6 +348,10 @@ void hmp_info_block(Monitor *mon, const QDict *qdict) > BlockdevDetectZeroesOptions_lookup[info->value->inserted->detect_zeroes]); > } > > + if (!info->value->inserted->write_merging) { > + monitor_printf(mon, " Write Merging: off\n"); > + } > + Currently, write_merging == true is the default; but as you yourself describe in block-core.json, this may change. I think always printing ths field's value would be fine, too. > if (info->value->inserted->bps > || info->value->inserted->bps_rd > || info->value->inserted->bps_wr > diff --git a/include/block/block_int.h b/include/block/block_int.h > index 8898c6c..e3d382f 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -402,6 +402,7 @@ struct BlockDriverState { > > QDict *options; > BlockdevDetectZeroesOptions detect_zeroes; > + bool write_merging; > > /* The error object in use for blocking operations on backing_hd */ > Error *backing_blocker; > diff --git a/qapi/block-core.json b/qapi/block-core.json > index 952d50e..9ac9085 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) > +# If this is 2.2, patch 1 must say 2.2 as well. > # @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', > @@ -1187,6 +1190,10 @@ > # (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) I'd ignore the parenthesis for alignment (which means remove one space in front of "depending"), but I don't object either. > # > # Since: 1.7 > ## > @@ -1200,7 +1207,8 @@ > '*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", Reviewed-by: Max Reitz <mreitz@redhat.com>
diff --git a/block.c b/block.c index 3b4a59a..ffb2b47 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)", }, { /* end of list */ } }, @@ -985,6 +989,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file, bs->drv = drv; bs->opaque = g_malloc0(drv->instance_size); bs->enable_write_cache = !!(flags & BDRV_O_CACHE_WB); + bs->write_merging = qemu_opt_get_bool(opts, "write-merging", true); /* Open the image, either directly or using a protocol */ if (drv->bdrv_file_open) { @@ -4439,6 +4444,10 @@ static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs, { int i, outidx; + if (!bs->write_merging) { + return num_reqs; + } + // Sort requests by start sector qsort(reqs, num_reqs, sizeof(*reqs), &multiwrite_req_compare); diff --git a/block/qapi.c b/block/qapi.c index a0f26e9..5f09967 100644 --- a/block/qapi.c +++ b/block/qapi.c @@ -59,6 +59,7 @@ BlockDeviceInfo *bdrv_block_device_info(BlockDriverState *bs) info->backing_file_depth = bdrv_get_backing_file_depth(bs); info->detect_zeroes = bs->detect_zeroes; + info->write_merging = bs->write_merging; if (bs->io_limits_enabled) { ThrottleConfig cfg; diff --git a/hmp.c b/hmp.c index baaa9e5..5762444 100644 --- a/hmp.c +++ b/hmp.c @@ -348,6 +348,10 @@ void hmp_info_block(Monitor *mon, const QDict *qdict) BlockdevDetectZeroesOptions_lookup[info->value->inserted->detect_zeroes]); } + if (!info->value->inserted->write_merging) { + monitor_printf(mon, " Write Merging: off\n"); + } + if (info->value->inserted->bps || info->value->inserted->bps_rd || info->value->inserted->bps_wr diff --git a/include/block/block_int.h b/include/block/block_int.h index 8898c6c..e3d382f 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -402,6 +402,7 @@ struct BlockDriverState { QDict *options; BlockdevDetectZeroesOptions detect_zeroes; + bool write_merging; /* The error object in use for blocking operations on backing_hd */ Error *backing_blocker; diff --git a/qapi/block-core.json b/qapi/block-core.json index 952d50e..9ac9085 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', @@ -1187,6 +1190,10 @@ # (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 ## @@ -1200,7 +1207,8 @@ '*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 block layer silently merges write requests since commit 40b4f539. This patch adds a knob to disable this feature as there has been some discussion lately if multiwrite is a good idea at all and as it falsifies benchmarks. Signed-off-by: Peter Lieven <pl@kamp.de> --- block.c | 9 +++++++++ block/qapi.c | 1 + hmp.c | 4 ++++ include/block/block_int.h | 1 + qapi/block-core.json | 10 +++++++++- qemu-options.hx | 1 + qmp-commands.hx | 2 ++ 7 files changed, 27 insertions(+), 1 deletion(-)