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Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_z
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes |
Date: |
Tue, 06 May 2014 20:52:20 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 |
On 05/06/2014 06:23 PM, Peter Lieven wrote:
> this patch tries to optimize zero write requests
> by automatically using bdrv_write_zeroes if it is
> supported by the format.
>
> This significantly speeds up file system initialization and
> should speed zero write test used to test backend storage
> performance.
>
>
> Signed-off-by: Peter Lieven <address@hidden>
> ---
> v2->v3: - moved parameter parsing to blockdev_init
> - added per device detect_zeroes status to
> hmp (info block -v) and qmp (query-block) [Eric]
> - added support to enable detect-zeroes also
> for hot added devices [Eric]
> - added missing entry to qemu_common_drive_opts
> - fixed description of qemu_iovec_is_zero [Fam]
>
>
> +static BdrvDetectZeroes parse_detect_zeroes(const char *buf, Error **errp)
> +{
> + if (!buf || !strcmp(buf, "off")) {
> + return BDRV_DETECT_ZEROES_OFF;
> + } else if (!strcmp(buf, "on")) {
> + return BDRV_DETECT_ZEROES_ON;
> + } else if (!strcmp(buf, "unmap")) {
> + return BDRV_DETECT_ZEROES_UNMAP;
> + } else {
> + error_setg(errp, "invalid value for detect-zeroes: %s",
> + buf);
> + }
> + return BDRV_DETECT_ZEROES_OFF;
> +}
Isn't there QAPI generated code that you can use instead of open-coding
this conversion between string and enum values?
> +++ b/qapi-schema.json
> @@ -937,6 +937,8 @@
> # @encryption_key_missing: true if the backing device is encrypted but an
> # valid encryption key is missing
> #
> +# @detect_zeroes: detect and optimize zero writes (Since 2.1)
> +#
> # @bps: total throughput limit in bytes per second is specified
> #
> # @bps_rd: read throughput limit in bytes per second is specified
> @@ -972,6 +974,7 @@
> 'data': { 'file': 'str', '*node-name': 'str', 'ro': 'bool', 'drv': 'str',
> '*backing_file': 'str', 'backing_file_depth': 'int',
> 'encrypted': 'bool', 'encryption_key_missing': 'bool',
> + 'detect_zeroes': 'str',
For new additions, we try to prefer dash over underscore. Eww - we've
already been inconsistent in this struct, with backing_file vs. node-name.
Maybe s/detect_zeroes/detect-zeroes/. I obviously can't argue too
strongly in light of the rest of the struct in isolation. However, you
DID use detect-zeroes on the input side later in the patch, so being
consistent between the two sites would be nice (given that node-name was
named consistently).
On the other hand, I _can_ argue strongly that open-coding this as 'str'
is wrong. You already added an enum type, so use it:
'detect_zeroes': 'BlockdevDetectZeroesOptions',
(hmm, in this context, it's not really an option, so maybe there is some
other name we can bikeshed about; but beyond 'BlockdevDetectZeroes', I
don't have any other good ideas)
zero is one of those odd words with two different pluralized spellings
both in common use. Code base currently has a 1:2 ratio between 'zeros'
vs. 'zeroes', so I guess you're okay; on the other hand, 'man qemu-img'
documents that 'convert -S' detects "zeros".
> 'bps': 'int', 'bps_rd': 'int', 'bps_wr': 'int',
> 'iops': 'int', 'iops_rd': 'int', 'iops_wr': 'int',
> 'image': 'ImageInfo',
> @@ -4250,6 +4253,20 @@
> 'data': [ 'ignore', 'unmap' ] }
>
> ##
> +# @BlockdevDetectZeroesOptions
> +#
> +# Selects the operation mode for zero write detection.
s/Selects/Describes/ since you are also going to use this enum on the
output field.
> +#
> +# @off: Disabled
> +# @on: Enabled
Maybe more details? Seeing this doesn't tell me the tradeoffs involved
in tweaking the parameter (one is faster, while the other uses less
storage resources - so maybe mention those benefits). I see the
documentation later on for the command line, so maybe repeating some of
that here would help someone going by just the QMP interface.
> +# @unmap: Enabled and even try to unmap blocks if possible
> +#
> +# Since: 2.1
> +##
> +{ 'enum': 'BlockdevDetectZeroesOptions',
> + 'data': [ 'off', 'on', 'unmap' ] }
> +
> +##
> # @BlockdevAioOptions
> #
> # Selects the AIO backend to handle I/O requests
> @@ -4327,7 +4346,8 @@
> '*aio': 'BlockdevAioOptions',
> '*rerror': 'BlockdevOnError',
> '*werror': 'BlockdevOnError',
> - '*read-only': 'bool' } }
> + '*read-only': 'bool',
> + '*detect-zeroes': 'BlockdevDetectZeroesOptions' } }
This part is fine.
> @var{copy-on-read} is "on" or "off" and enables whether to copy read backing
> file sectors into the image file.
> address@hidden address@hidden
> address@hidden is "off", "on" or "unmap" and enables the automatic
> +conversion of plain zero writes by the OS to driver specific optimized
> +zero write commands. If "unmap" is chosen and @var{discard} is "on"
> +a zero write may even be converted to an UNMAP operation.
This looks good.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Peter Lieven, 2014/05/06
- [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Peter Lieven, 2014/05/06
- Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes,
Eric Blake <=
- Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Peter Lieven, 2014/05/07
- Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Kevin Wolf, 2014/05/07
- Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Peter Lieven, 2014/05/07
- Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Kevin Wolf, 2014/05/07
- Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Peter Lieven, 2014/05/07
- Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Peter Lieven, 2014/05/07
- Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Kevin Wolf, 2014/05/08
- Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes, Peter Lieven, 2014/05/07