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cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Wed, 9 Sep 2020 11:13:42 +0800 Received: from zxbjmbx1.zhaoxin.com (10.29.252.163) by zxbjmbx2.zhaoxin.com (10.29.252.164) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Wed, 9 Sep 2020 11:13:41 +0800 Received: from zxbjmbx1.zhaoxin.com ([fe80::290a:f538:51e7:1416]) by zxbjmbx1.zhaoxin.com ([fe80::290a:f538:51e7:1416%16]) with mapi id 15.01.1979.003; Wed, 9 Sep 2020 11:13:41 +0800 From: RockCui-oc To: Max Reitz , John Snow , "qemu-devel@nongnu.org" Subject: =?gb2312?B?tPC4tDogW1BBVENIXSBpZGU6ZG8gbm90aGluZyBmb3IgaWRlbnRpZnkgY21k?= =?gb2312?Q?_if_no_any_device_attached?= Thread-Topic: [PATCH] ide:do nothing for identify cmd if no any device attached Thread-Index: AQHWdEfWn1VcMPOnkU+PO9h+3wgKR6lVN70AgAEW7ACACXBwng== Date: Wed, 9 Sep 2020 03:13:41 +0000 Message-ID: <4ee746f7bb364ed491d2b00a9b810183@zhaoxin.com> References: <20200817033803.14014-1-RockCui-oc@zhaoxin.com> 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Hi John & Max=A3=AC


  1. Follow my Log=A3=ACthere are 10000 read 0x1x7 ops. On my Intel I5 platf= orm, if down the frequency to 1.2G, you can see a obviously lag during WIND= OWS LOGO animation playing.
  2. We must supply a CD-ROM to our VDI user= s.
  3. In ide_ioport_read() :
----------------------------------------------------------------------= -----------------------------
case 7:
       if ((!bus->ifs[0].blk && !b= us->ifs[1].blk) || (s !=3D bus->ifs && !s->blk)) {
            ret =3D = 0;
       } else {
            ret =3D = s->status;
       }
----------------------------------------------------------------------= ------------------------------
            so I follow this.

Rock 



=B7=A2=BC=FE=C8=CB: Max R= eitz <mreitz@redhat.com>
=B7=A2=CB=CD=CA=B1=BC=E4: 2020=C4=EA9=D4=C23=C8=D5 18:40
=CA=D5=BC=FE=C8=CB: John Snow; RockCui-oc; qemu-devel@nongnu.org
=B3=AD=CB=CD: Cobe Chen(BJ-RD); Peter Maydell
=D6=F7=CC=E2: Re: [PATCH] ide:do nothing for identify cmd if no any = device attached
 
On 02.09.20 20:02, John Snow wrote:
> (CC Max for block backend model confusion, see below)
>
> On 8/16/20 11:38 PM, zhaoxin\RockCuioc wrote:
>> This patch is for avoiding win7 IDE driver polling 0x1f7 when
>> no any device attached. During Win7 VM boot procedure, if use virt= io for
>> disk and there is no any device be attached on hda & hdb, the = win7 IDE
>> driver
>> would poll 0x1f7 for a while. This action may be stop windows LOGO=
>> atomic for
>> a while too on a poor performance CPU.
>>
>
> A few questions:
>
> (1) How slow is the probing?
>
> (2) If there are no devices attached, why don't you remove the IDE
> controller so that Windows doesn't have to probe it?
>
>> Signed-off-by: zhaoxin\RockCuioc <RockCui-oc@zhaoxin.com> >> ---
>>   hw/ide/core.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/ide/core.c b/hw/ide/core.c
>> index d997a78e47..26d86f4b40 100644
>> --- a/hw/ide/core.c
>> +++ b/hw/ide/core.c
>> @@ -2073,8 +2073,9 @@ void ide_exec_cmd(IDEBus *bus, uint32_t = val)
>>       s =3D idebus_active_if(bus);
>>       trace_ide_exec_cmd(bus, s, val); >>   -    /* ignore commands to non existent slav= e */
>> -    if (s !=3D bus->ifs && !s->blk) = {

(Was the first one basically meant to be =A1=B0s !=3D &bus->ifs[0]= =A1=B1, i.e. to
check that this doesn=A1=AFt go to the ma^W primary?  Not too obvious.= )

>> +    /* ignore commands if no any device exist = or non existent slave */
>> +    if ((!bus->ifs[0].blk && !bus-&= gt;ifs[1].blk) ||
>> +        (s !=3D bus->if= s && !s->blk)) {

(Maybe this could be improved here)

>>           return;
>>       }
>>  
>
> I think it's the case that Empty CD-ROM drives will have an anonymous<= br> > block backend representing the empty drive,

(As far as I remember,) yes.

(ide_dev_initfn() ensures all CD drives have one, even if it=A1=AFs empty.)=

> so I suppose this is maybe
> fine?
>
> I suppose the idea is that with no drives on the bus that it's fine to=
> ignore the register writes, as there are no devices to record those wr= ites.
>
> (But then, why did we ever only check device1? ...)
>
> Maybe before the block-backend split we used to have to check to see i= f
> we had attached media or not, but I think nowadays we should always ha= ve
> a blk pointer if we have a device model intended to be operating at th= is
> address.

The check in ide_dev_initfn() looks that way to me.

> So I guess it can be simplified ...?
>
> if (!s->blk) {
>     return;
> }

Probably.  Although there=A1=AFs a difference, of course, namely if yo= u have
only a secondary device and try to access the primary, this simplified
version will be a no-op, whereas the more complicated version in this
patch would still go on.  I don=A1=AFt know how real hardware would ha= ndle
that case.  Is it even possible to have just a secondary with no prima= ry?

Max

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