diff options
| author | Peter Lieven <pl@kamp.de> | 2014-05-18 00:58:19 +0200 |
|---|---|---|
| committer | Kevin Wolf <kwolf@redhat.com> | 2014-05-19 13:42:27 +0200 |
| commit | 465bee1da82e43f18d10c43cc7566d0284ad13a9 (patch) | |
| tree | c98c26268e8f10a77bfc39abb72f72f8c7ac9ee8 /qemu-options.hx | |
| parent | 82a402e99f3f8c6177528ad6d561bf07ff6ee606 (diff) | |
block: optimize zero writes with bdrv_write_zeroes
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.
I ran the following 2 tests on my internal SSD with a
50G QCOW2 container and on an attached iSCSI storage.
a) mkfs.ext4 -E lazy_itable_init=0,lazy_journal_init=0 /dev/vdX
QCOW2 [off] [on] [unmap]
-----
runtime: 14secs 1.1secs 1.1secs
filesize: 937M 18M 18M
iSCSI [off] [on] [unmap]
----
runtime: 9.3s 0.9s 0.9s
b) dd if=/dev/zero of=/dev/vdX bs=1M oflag=direct
QCOW2 [off] [on] [unmap]
-----
runtime: 246secs 18secs 18secs
filesize: 51G 192K 192K
throughput: 203M/s 2.3G/s 2.3G/s
iSCSI* [off] [on] [unmap]
----
runtime: 8mins 45secs 33secs
throughput: 106M/s 1.2G/s 1.6G/s
allocated: 100% 100% 0%
* The storage was connected via an 1Gbit interface.
It seems to internally handle writing zeroes
via WRITESAME16 very fast.
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'qemu-options.hx')
| -rw-r--r-- | qemu-options.hx | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/qemu-options.hx b/qemu-options.hx index 7587bce5c8..c2c0823911 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -414,6 +414,7 @@ DEF("drive", HAS_ARG, QEMU_OPTION_drive, " [,serial=s][,addr=A][,rerror=ignore|stop|report]\n" " [,werror=ignore|stop|report|enospc][,id=name][,aio=threads|native]\n" " [,readonly=on|off][,copy-on-read=on|off]\n" + " [,detect-zeroes=on|off|unmap]\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" @@ -475,6 +476,11 @@ Open drive @option{file} as read-only. Guest write attempts will fail. @item copy-on-read=@var{copy-on-read} @var{copy-on-read} is "on" or "off" and enables whether to copy read backing file sectors into the image file. +@item detect-zeroes=@var{detect-zeroes} +@var{detect-zeroes} is "off", "on" or "unmap" and enables the automatic +conversion of plain zero writes by the OS to driver specific optimized +zero write commands. You may even choose "unmap" if @var{discard} is set +to "unmap" to allow a zero write to be converted to an UNMAP operation. @end table By default, the @option{cache=writeback} mode is used. It will report data |