Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD

[Peter Maydell]

On 17 March 2013 10:17, Aurelien Jarno <address@hidden> wrote:
> On Sun, Mar 17, 2013 at 12:23:31AM +0000, Peter Maydell wrote:
>> On 17 March 2013 00:04, Aurelien Jarno <address@hidden> wrote:
>> > On Fri, Mar 15, 2013 at 03:45:11PM +0000, Peter Maydell wrote:
>> >> I agree we shouldn't be claiming to have a scsi interface, yes.
>> >>
>> >
>> > Does it means you are going to accept the patch?
>>
>> No, I meant I'd accept a patch which stops us reporting that
>> we have a SCSI interface when we don't.
>
> That's what the patch does, by correctly saying it's an SD interface and
> not a SCSI one.

The patch does two things:
 * stops claiming a default SCSI interface [obviously right]
 * starts claiming a default SD interface [what we're arguing about]

>> > In anycase let me give you some more arguments in favor of it. Even if
>> > you believe that users should always provide a cache= argument, I don't
>> > think it should be done by setting a wrong default interfaces. Users are
>> > likely to simply google for a command line and paste it without
>> > understanding the consequences of cache=writeback. The way to go there
>> > is to make the writeback argument mandatory for some machines if you
>> > really believe it's need by all users.
>>
>> writeback shouldn't be mandatory randomly for some machines and
>> interfaces and not others.
>
> I don't get your point there. You don't want to make it mandatory at the
> QEMU level, but you want users to understand they have to specify it for
> some machines, by making if= mandatory randomly for some machines and
> not others?

My point is that I don't think there's a good solution to "modelled SD
cards aren't a good substitute for modelled hard disks".

That said, I want to postpone the rest of this conversation until I've
had a chance to look into what has changed regarding performance of
SD with the default cache settings.

-- PMM