From: Paolo Bonzini <pbonzini@redhat.com>
To: "Richard W.M. Jones" <rjones@redhat.com>
Cc: Teng-Feng Yang <shinrairis@gmail.com>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] TRIM/DISCARD/UNMAP support on qemu-nbd
Date: Thu, 09 Jan 2014 08:02:23 +0100 [thread overview]
Message-ID: <52CE497F.7020808@redhat.com> (raw)
In-Reply-To: <20140108225354.GQ4802@redhat.com>
Il 08/01/2014 23:53, Richard W.M. Jones ha scritto:
> On Wed, Jan 08, 2014 at 11:45:39PM +0100, Paolo Bonzini wrote:
>> Il 08/01/2014 23:24, Richard W.M. Jones ha scritto:
>>> It's extremely difficult to know when it's safe to add this parameter.
>>> Qemu gives no indication of when using discard=.. is safe (ie. won't
>>> cause qemu to fail to start up or fail in some other way). It's even
>>> worse when we have to go via libvirt which itself doesn't expose
>>> qemu's capabilities upwards.
>>
>> It is a bug that "-help" doesn't list discard=on, but QMP
>> query-command-line-options lists it correctly.
>>
>> libvirt could safely ignore discard if the underlying QEMU does not
>> support it, but that's not how it was implemented. Currently,
>> explicitly specifying either discard='on' and discard='off' will cause
>> the VM to fail to start if QEMU does not support it. There are
>> tradeoffs in both solutions...
>
> That sucks .. for me ...
>
> Can't we have an option like discard=ifpossible? libguestfs would use
> this, since we'd always prefer to honour discard requests from our
> kernel.
That would be a libvirt option, not QEMU.
Paolo
next prev parent reply other threads:[~2014-01-09 7:02 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-30 11:58 [Qemu-devel] TRIM/DISCARD/UNMAP support on qemu-nbd Teng-Feng Yang
2014-01-02 16:15 ` Richard W.M. Jones
2014-01-07 14:48 ` Paolo Bonzini
2014-01-07 20:27 ` Richard W.M. Jones
2014-01-07 20:48 ` Paolo Bonzini
2014-01-07 21:22 ` Richard W.M. Jones
2014-01-08 22:11 ` Paolo Bonzini
2014-01-08 22:24 ` Richard W.M. Jones
2014-01-08 22:45 ` Paolo Bonzini
2014-01-08 22:53 ` Richard W.M. Jones
2014-01-09 7:02 ` Paolo Bonzini [this message]
2014-01-07 21:27 ` Richard W.M. Jones
2014-01-06 2:45 ` Stefan Hajnoczi
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