Both qemu and qemu-img use writeback cache mode by default, which is
already documented in qemu(1). qemu-nbd uses writethrough cache mode by
default, and the default cache mode is not documented.
According to the qemu-nbd(8):
--cache=CACHE
The cache mode to be used with the file. See the
documentation of the emulator's -drive cache=... option for
allowed values.
qemu(1) says:
The default mode is cache=writeback.
So users have no reason to assume that qemu-nbd is using writethough
cache mode. The only hint is the painfully slow writing when using the
defaults.
Looking in git history, it seems that qemu used writethrough in the past
to support broken guests that did not flush data properly, or could not
flush due to limitations in qemu. But qemu-nbd clients can use
NBD_CMD_FLUSH to flush data, so using writethrough does not help anyone.
Change the default cache mode to writback, and document the default and
available values properly in the online help and manual.
With this change converting image via qemu-nbd is 3.5 times faster.
$ qemu-img create dst.img 50g
$ qemu-nbd -t -f raw -k /tmp/nbd.sock dst.img
Before this change:
$ hyperfine -r3 "./qemu-img convert -p -f raw -O raw -T none -W fedora34.img nbd+unix:///?socket=/tmp/nbd.sock"
Benchmark #1: ./qemu-img convert -p -f raw -O raw -T none -W fedora34.img nbd+unix:///?socket=/tmp/nbd.sock
Time (mean ± σ): 83.639 s ± 5.970 s [User: 2.733 s, System: 6.112 s]
Range (min … max): 76.749 s … 87.245 s 3 runs
After this change:
$ hyperfine -r3 "./qemu-img convert -p -f raw -O raw -T none -W fedora34.img nbd+unix:///?socket=/tmp/nbd.sock"
Benchmark #1: ./qemu-img convert -p -f raw -O raw -T none -W fedora34.img nbd+unix:///?socket=/tmp/nbd.sock
Time (mean ± σ): 23.522 s ± 0.433 s [User: 2.083 s, System: 5.475 s]
Range (min … max): 23.234 s … 24.019 s 3 runs
Users can avoid the issue by using --cache=writeback[1] but the defaults
should give good performance for the common use case.
[1] https://bugzilla.redhat.com/1990656
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Message-Id: <20210813205519.50518-1-nsoffer@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit 0961525705)
Signed-off-by: Michael Roth <michael.roth@amd.com>
These HMP commands had been removed/replaced in QEMU v2.12. Still, some
people might want to update from older versions to the recent QEMU version,
so we should give some recommendations for the replacements in our
documentation.
Message-Id: <20210811084103.74832-5-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
These CLI options had been removed/replaced in QEMU v3.1. Still, some
people might want to update from older versions to the recent QEMU version,
so we should give some recommendations for the replacements in our
documentation.
Message-Id: <20210811084103.74832-4-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
These CLI options had been removed/replaced in QEMU v3.0. Still, some
people might want to update from older versions to the recent QEMU version,
so we should give some recommendations for the replacements in our
documentation.
Message-Id: <20210811084103.74832-3-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
These CLI options had been removed/replaced in QEMU v2.12. Still, some
people might want to update from older versions to the recent QEMU version,
so we should give some recommendations for the replacements in our
documentation.
Message-Id: <20210811084103.74832-2-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
This is a very rudimentary conversion from .txt to .rst changing as
little as possible, but getting it to render somewhat nicely; without
using any Sphinx directives. (It is 'native' ReST.)
Further patches will add cross-references and Sphinx-specific extensions
to make it sparkle.
Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210720235619.2048797-2-jsnow@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Move bootindex.txt into the system section of the manual and turn it
into rST format. To make the document make more sense in the context
of the system manual, expand the title and introductory paragraphs to
give more context.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 20210727194955.7764-1-peter.maydell@linaro.org
In rST markup, single backticks `like this` represent "interpreted
text", which can be handled as a bunch of different things if tagged
with a specific "role":
https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text
(the most common one for us is "reference to a URL, which gets
hyperlinked").
The default "role" if none is specified is "title_reference",
intended for references to book or article titles, and it renders
into the HTML as <cite>...</cite> (usually comes out as italics).
This commit fixes various places in the manual which were
using single backticks when double backticks (for literal text)
were intended, and covers those files where only one or two
instances of these errors were made.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
In rST markup, single backticks `like this` represent "interpreted
text", which can be handled as a bunch of different things if tagged
with a specific "role":
https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text
(the most common one for us is "reference to a URL, which gets
hyperlinked").
The default "role" if none is specified is "title_reference",
intended for references to book or article titles, and it renders
into the HTML as <cite>...</cite> (usually comes out as italics).
To format a literal (generally rendered as fixed-width font),
double-backticks are required.
cpu-features.rst consistently uses single backticks when double backticks
are required; correct it.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20210726142338.31872-8-peter.maydell@linaro.org
In rST markup, single backticks `like this` represent "interpreted
text", which can be handled as a bunch of different things if tagged
with a specific "role":
https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text
(the most common one for us is "reference to a URL, which gets
hyperlinked").
The default "role" if none is specified is "title_reference",
intended for references to book or article titles, and it renders
into the HTML as <cite>...</cite> (usually comes out as italics).
To format a literal (generally rendered as fixed-width font),
double-backticks are required.
protvirt.rst consistently uses single backticks when double backticks
are required; correct it.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Message-id: 20210726142338.31872-7-peter.maydell@linaro.org
In rST markup, single backticks `like this` represent "interpreted
text", which can be handled as a bunch of different things if tagged
with a specific "role":
https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text
(the most common one for us is "reference to a URL, which gets
hyperlinked").
The default "role" if none is specified is "title_reference",
intended for references to book or article titles, and it renders
into the HTML as <cite>...</cite> (usually comes out as italics).
Fix various places in the devel section of the manual which were
using single backticks when double backticks (for literal text)
were intended.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20210726142338.31872-6-peter.maydell@linaro.org
In rST markup, single backticks `like this` represent "interpreted
text", which can be handled as a bunch of different things if tagged
with a specific "role":
https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text
(the most common one for us is "reference to a URL, which gets
hyperlinked").
The default "role" if none is specified is "title_reference",
intended for references to book or article titles, and it renders
into the HTML as <cite>...</cite> (usually comes out as italics).
To format a literal (generally rendered as fixed-width font),
double-backticks are required.
Mostly migration.rst gets this right, but some places incorrectly use
single backticks where double backticks were intended; correct them.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-id: 20210726142338.31872-5-peter.maydell@linaro.org
In rST markup, single backticks `like this` represent "interpreted
text", which can be handled as a bunch of different things if tagged
with a specific "role":
https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text
(the most common one for us is "reference to a URL, which gets
hyperlinked").
The default "role" if none is specified is "title_reference",
intended for references to book or article titles, and it renders
into the HTML as <cite>...</cite> (usually comes out as italics).
To format a literal (generally rendered as fixed-width font),
double-backticks are required.
ebpf_rss.rst gets this wrong in a few places; correct them.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20210726142338.31872-4-peter.maydell@linaro.org
One of the example meson.build fragments incorrectly quotes some
symbols as 'CONFIG_FOO`; the correct syntax here is 'CONFIG_FOO'.
(This isn't a rST formatting mistake because the example is displayed
literally; it's just the wrong kind of quote.)
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20210726142338.31872-3-peter.maydell@linaro.org
In rST markup, single backticks `like this` represent "interpreted
text", which can be handled as a bunch of different things if tagged
with a specific "role":
https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text
(the most common one for us is "reference to a URL, which gets
hyperlinked").
The default "role" if none is specified is "title_reference",
intended for references to book or article titles, and it renders
into the HTML as <cite>...</cite> (usually comes out as italics).
build-system.rst seems to have been written under the mistaken
assumption that single-backticks mark up literal text (function
names, etc) which should be rendered in a fixed-width font.
The rST markup for this is ``double backticks``.
Update all the markup.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210726142338.31872-2-peter.maydell@linaro.org
Our built HTML documentation now has a standard footer which
gives the license for QEMU (and its documentation as a whole).
In almost all pages, we either don't bother to state the
copyright/license for the individual rST sources, or we put
it in an rST comment. There are just three pages which render
copyright or license information into the user-visible HTML.
Quoting a specific (different) license for an individual HTML
page within the manual is confusing. Downgrade the license
and copyright info to a comment within the rST source, bringing
these pages in line with the rest of our documents.
Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-id: 20210722192016.24915-3-peter.maydell@linaro.org
We already have a section on USB in the rST manual; fold
the information in docs/usb-storage.txt into it.
We add 'format=raw' to the various -drive options in the code
examples, because QEMU will print warnings these days if you
omit it.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20210728141457.14825-2-peter.maydell@linaro.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
While we do mention some of this stuff in the various daemons and
manuals the subtleties of the socket and memory sharing are sometimes
missed. This document attempts to give some background on vhost-user
daemons in general terms.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20210720232703.10650-4-alex.bennee@linaro.org>
The point of 'qemu-img convert --bitmaps' is to be a convenience for
actions that are already possible through a string of smaller
'qemu-img bitmap' sub-commands. One situation not accounted for
already is that if a source image contains an inconsistent bitmap (for
example, because a qemu process died abruptly before flushing bitmap
state), the user MUST delete those inconsistent bitmaps before
anything else useful can be done with the image.
We don't want to delete inconsistent bitmaps by default: although a
corrupt bitmap is only a loss of optimization rather than a corruption
of user-visible data, it is still nice to require the user to opt in
to the fact that they are aware of the loss of the bitmap. Still,
requiring the user to check 'qemu-img info' to see whether bitmaps are
consistent, then use 'qemu-img bitmap --remove' to remove offenders,
all before using 'qemu-img convert', is a lot more work than just
adding a knob 'qemu-img convert --bitmaps --skip-broken-bitmaps' which
opts in to skipping the broken bitmaps.
After testing the new option, also demonstrate the way to manually fix
things (either deleting bad bitmaps, or re-creating them as empty) so
that it is possible to convert without the option.
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1946084
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210709153951.2801666-4-eblake@redhat.com>
[eblake: warning message tweak, test enhancements]
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Add a line to the HTML document footer mentioning the QEMU version.
The version information is already provided in very faint text below
the QEMU logo in the sidebar, but that is rather inconspicious, so
repeating it in the footer seems useful.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20210705095547.15790-8-peter.maydell@linaro.org
The standard Sphinx/RTD HTML page footer gives a copyright line
(based on the 'copyright' variable set in conf.py) and a line "Built
with Sphinx using a theme provided by Read the Docs" (which can be
disabled via the html_show_sphinx variable, but we leave it enabled).
As a free software project, we'd like to also mention the license
QEMU and its manual are released under.
Add a template footer.html which defines the 'extrafooter' block that
the RtD theme provides for this purpose. The new line of text will
go below the existing copyright and sphinx-acknowledgement lines.
(Unfortunately the RTD footer template does not permit putting it
after the copyright but before the sphinx-acknowledgement.)
We use the templating functionality to make the new text also be a
hyperlink to the about/license.html page of the manual.
Unlike rst files, HTML template files are not reported to our depfile
plugin, so we maintain a manual list in meson.build. New template
files should be rare, so not being able to auto-generate the
dependency info is not too awkward.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20210705095547.15790-7-peter.maydell@linaro.org
Now that we have a single Sphinx manual rather than multiple manuals,
we can provide a better place for "common to all of QEMU" information
like the deprecation notices, build platforms, license information,
which we currently have in the system/ manual even though it applies
to all of QEMU.
Create a new directory about/ on the same level as system/, user/,
etc, and move these documents there.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20210705095547.15790-5-peter.maydell@linaro.org
We merged our previous multiple-manual setup into a single Sphinx
manual, but we left some text in the various index.rst lines that
still calls the top level subsections separate 'manuals'. Update
them to talk about "this section of the manual" instead, and remove
now-obsolete comments about how the index.rst files are the "top
level page for the 'foo' manual".
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20210705095547.15790-3-peter.maydell@linaro.org
