From: Eric Blake <eblake@redhat.com>
To: Nir Soffer <nsoffer@redhat.com>
Cc: qemu-block <qemu-block@nongnu.org>,
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
QEMU Developers <qemu-devel@nongnu.org>,
Nir Soffer <nirsof@gmail.com>,
qemu-stable@nongnu.org
Subject: Re: [PATCH] qemu-nbd: Change default cache mode to writeback
Date: Mon, 20 Sep 2021 11:52:12 -0500 [thread overview]
Message-ID: <20210920165212.la2z7pyizm4sv4t4@redhat.com> (raw)
In-Reply-To: <CAMRbyytKnLWFm7G5-bq5A-3nny63ESoxYYQt4sigYg2c4f9Ryg@mail.gmail.com>
On Sun, Sep 19, 2021 at 10:56:58PM +0300, Nir Soffer wrote:
> On Mon, Aug 16, 2021 at 6:50 PM Eric Blake <eblake@redhat.com> wrote:
> >
> > On Fri, Aug 13, 2021 at 11:55:19PM +0300, Nir Soffer wrote:
> > > 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.
> >
> > Oh, good catch. Unfortunately too late for 6.1 proper, but I'll add
> > qemu-stable in cc and queue this through my NBD tree for 6.2.
>
> I don't see this in master, lost in your NBD tree?
It's on my tree:
https://repo.or.cz/qemu/ericb.git/shortlog/refs/heads/nbd
I just haven't bundled up enough patches for a pull request yet. I'll
get one out this week, probably with a few more patches included.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
prev parent reply other threads:[~2021-09-20 17:08 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-13 20:55 [PATCH] qemu-nbd: Change default cache mode to writeback Nir Soffer
2021-08-16 15:50 ` Eric Blake
2021-09-19 19:56 ` Nir Soffer
2021-09-20 16:52 ` Eric Blake [this message]
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