From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50275) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xg8oE-00068c-DU for qemu-devel@nongnu.org; Mon, 20 Oct 2014 04:59:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xg8o9-0003eA-5O for qemu-devel@nongnu.org; Mon, 20 Oct 2014 04:59:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26266) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xg8o8-0003e4-TF for qemu-devel@nongnu.org; Mon, 20 Oct 2014 04:59:17 -0400 Message-ID: <5444CED9.8070402@redhat.com> Date: Mon, 20 Oct 2014 10:59:05 +0200 From: Max Reitz MIME-Version: 1.0 References: <1413785643-20336-1-git-send-email-pl@kamp.de> In-Reply-To: <1413785643-20336-1-git-send-email-pl@kamp.de> Content-Type: text/plain; charset=iso-8859-15; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] block: add a knob to disable multiwrite_merge List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven , qemu-devel@nongnu.org Cc: kwolf@redhat.com, famz@redhat.com, armbru@redhat.com, stefanha@redhat.com On 2014-10-20 at 08:14, Peter Lieven wrote: > the block layer silently merges write requests since 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 > --- > block.c | 4 ++++ > block/qapi.c | 1 + > blockdev.c | 7 +++++++ > hmp.c | 4 ++++ > include/block/block_int.h | 1 + > qapi/block-core.json | 10 +++++++++- > qemu-options.hx | 1 + > qmp-commands.hx | 2 ++ > 8 files changed, 29 insertions(+), 1 deletion(-) > > diff --git a/block.c b/block.c > index 27533f3..1658a72 100644 > --- a/block.c > +++ b/block.c > @@ -4531,6 +4531,10 @@ 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 9733ebd..02251dd 100644 > --- a/block/qapi.c > +++ b/block/qapi.c > @@ -58,6 +58,7 @@ 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/blockdev.c b/blockdev.c > index e595910..13e47b8 100644 > --- a/blockdev.c > +++ b/blockdev.c > @@ -378,6 +378,7 @@ static DriveInfo *blockdev_init(const char *file, QDict *bs_opts, > const char *id; > bool has_driver_specific_opts; > BlockdevDetectZeroesOptions detect_zeroes; > + bool write_merging; > BlockDriver *drv = NULL; > > /* Check common options by copying from bs_opts to opts, all other options > @@ -405,6 +406,7 @@ static DriveInfo *blockdev_init(const char *file, QDict *bs_opts, > snapshot = qemu_opt_get_bool(opts, "snapshot", 0); > ro = qemu_opt_get_bool(opts, "read-only", 0); > copy_on_read = qemu_opt_get_bool(opts, "copy-on-read", false); > + write_merging = qemu_opt_get_bool(opts, "write-merging", true); Using this option in blockdev_init() means that you can only enable or disable merging for the top layer (the root BDS). Furthermore, since you don't set bs->write_merging in bdrv_new() (or at least bdrv_open()), it actually defaults to false and only for the top layer it defaults to true. Therefore, if after this patch a format block driver issues a multiwrite to its file, the write will not be merged and the user can do nothing about it. I don't suppose this is intentional...? I propose evaluating the option in bdrv_open() and setting bs->write_merging there. > if ((buf = qemu_opt_get(opts, "discard")) != NULL) { > if (bdrv_parse_discard_flags(buf, &bdrv_flags) != 0) { > @@ -530,6 +532,7 @@ static DriveInfo *blockdev_init(const char *file, QDict *bs_opts, > bs->open_flags = snapshot ? BDRV_O_SNAPSHOT : 0; > bs->read_only = ro; > bs->detect_zeroes = detect_zeroes; > + bs->write_merging = write_merging; > > bdrv_set_on_error(bs, on_read_error, on_write_error); > > @@ -2746,6 +2749,10 @@ QemuOptsList qemu_common_drive_opts = { > .name = "detect-zeroes", > .type = QEMU_OPT_STRING, > .help = "try to optimize zero writes (off, on, unmap)", > + },{ > + .name = "write-merging", > + .type = QEMU_OPT_BOOL, > + .help = "enable write merging (default: true)", > }, > { /* end of list */ } > }, > diff --git a/hmp.c b/hmp.c > index 63d7686..8d6ad0b 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 8d86a6c..39bbde2 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -407,6 +407,7 @@ 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 8f7089e..4931bd9 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', > @@ -1180,6 +1183,10 @@ > # (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 > ## > @@ -1193,7 +1200,8 @@ > '*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..529a563 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 multiwrite_merge feature (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", Hm, thanks for reminding me of that file. There are some things which I forgot to update (ImageInfoSpecific at least)... Max