nvme: do not advertise support for unsupported arbitration mechanism

[Qemu-devel] [PATCH] nvme: do not advertise support for unsupported arbitration mechanism

Posted by Klaus Birkelund Jensen 4 years, 10 months ago

The device mistakenly reports that the Weighted Round Robin with Urgent
Priority Class arbitration mechanism is supported.

It is not.

Signed-off-by: Klaus Birkelund Jensen <klaus.jensen@cnexlabs.com>
---
 hw/block/nvme.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index 30e50f7a3853..415b4641d6b4 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -1383,7 +1383,6 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
     n->bar.cap = 0;
     NVME_CAP_SET_MQES(n->bar.cap, 0x7ff);
     NVME_CAP_SET_CQR(n->bar.cap, 1);
-    NVME_CAP_SET_AMS(n->bar.cap, 1);
     NVME_CAP_SET_TO(n->bar.cap, 0xf);
     NVME_CAP_SET_CSS(n->bar.cap, 1);
     NVME_CAP_SET_MPSMAX(n->bar.cap, 4);
-- 
2.21.0

Re: [Qemu-devel] [PATCH] nvme: do not advertise support for unsupported arbitration mechanism

Posted by Max Reitz 4 years, 10 months ago

On 06.06.19 11:25, Klaus Birkelund Jensen wrote:
> The device mistakenly reports that the Weighted Round Robin with Urgent
> Priority Class arbitration mechanism is supported.
> 
> It is not.

I believe you based on the fact that there is no “weight” or “priority”
anywhere in nvme.c, and that it does not evaluate the Arbitration
Mechanism Selected field.

> Signed-off-by: Klaus Birkelund Jensen <klaus.jensen@cnexlabs.com>
> ---
>  hw/block/nvme.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> index 30e50f7a3853..415b4641d6b4 100644
> --- a/hw/block/nvme.c
> +++ b/hw/block/nvme.c
> @@ -1383,7 +1383,6 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
>      n->bar.cap = 0;
>      NVME_CAP_SET_MQES(n->bar.cap, 0x7ff);
>      NVME_CAP_SET_CQR(n->bar.cap, 1);
> -    NVME_CAP_SET_AMS(n->bar.cap, 1);

I suppose the better way would be to pass 0, so it is more explicit, I
think.

(Just removing it looks like it may have just been forgotten.)

Max

>      NVME_CAP_SET_TO(n->bar.cap, 0xf);
>      NVME_CAP_SET_CSS(n->bar.cap, 1);
>      NVME_CAP_SET_MPSMAX(n->bar.cap, 4);
>

Re: [Qemu-devel] [Qemu-block] [PATCH] nvme: do not advertise support for unsupported arbitration mechanism

Posted by Maxim Levitsky 4 years, 10 months ago

On Fri, 2019-06-14 at 22:39 +0200, Max Reitz wrote:
> On 06.06.19 11:25, Klaus Birkelund Jensen wrote:
> > The device mistakenly reports that the Weighted Round Robin with Urgent
> > Priority Class arbitration mechanism is supported.
> > 
> > It is not.
> 
> I believe you based on the fact that there is no “weight” or “priority”
> anywhere in nvme.c, and that it does not evaluate the Arbitration
> Mechanism Selected field.
> 
> > Signed-off-by: Klaus Birkelund Jensen <klaus.jensen@cnexlabs.com>
> > ---
> >  hw/block/nvme.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> > index 30e50f7a3853..415b4641d6b4 100644
> > --- a/hw/block/nvme.c
> > +++ b/hw/block/nvme.c
> > @@ -1383,7 +1383,6 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
> >      n->bar.cap = 0;
> >      NVME_CAP_SET_MQES(n->bar.cap, 0x7ff);
> >      NVME_CAP_SET_CQR(n->bar.cap, 1);
> > -    NVME_CAP_SET_AMS(n->bar.cap, 1);
> 
> I suppose the better way would be to pass 0, so it is more explicit, I
> think.
> 
> (Just removing it looks like it may have just been forgotten.)
> 
> Max
> 
> >      NVME_CAP_SET_TO(n->bar.cap, 0xf);
> >      NVME_CAP_SET_CSS(n->bar.cap, 1);
> >      NVME_CAP_SET_MPSMAX(n->bar.cap, 4);
> > 
> 
> 

Yea. no way that this driver supports WRRU and I haven't noticed it.
Just checked again to be sure.

To be honest, after some quick look, 
that driver doesn' even really support the regular Round-Robin as it uses a timer to process a specific queue, 
kicked up by a doorbell write :-)


Acked-by: Maxim Levitsky <mlevitsk@redhat.com>


Best regards,
	Maxim Levitsky

Re: [Qemu-devel] [PATCH] nvme: do not advertise support for unsupported arbitration mechanism

Posted by Klaus Birkelund 4 years, 10 months ago

On Fri, Jun 14, 2019 at 10:39:27PM +0200, Max Reitz wrote:
> On 06.06.19 11:25, Klaus Birkelund Jensen wrote:
> > The device mistakenly reports that the Weighted Round Robin with Urgent
> > Priority Class arbitration mechanism is supported.
> > 
> > It is not.
> 
> I believe you based on the fact that there is no “weight” or “priority”
> anywhere in nvme.c, and that it does not evaluate the Arbitration
> Mechanism Selected field.
> 

Not sure if you want me to change the commit message? Feel free to
change it if you want to ;)

> > Signed-off-by: Klaus Birkelund Jensen <klaus.jensen@cnexlabs.com>
> > ---
> >  hw/block/nvme.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> > index 30e50f7a3853..415b4641d6b4 100644
> > --- a/hw/block/nvme.c
> > +++ b/hw/block/nvme.c
> > @@ -1383,7 +1383,6 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
> >      n->bar.cap = 0;
> >      NVME_CAP_SET_MQES(n->bar.cap, 0x7ff);
> >      NVME_CAP_SET_CQR(n->bar.cap, 1);
> > -    NVME_CAP_SET_AMS(n->bar.cap, 1);
> 
> I suppose the better way would be to pass 0, so it is more explicit, I
> think.
> 
> (Just removing it looks like it may have just been forgotten.)
> 

Not explicitly setting it to zero aligns with how the other fields in
CAP are also left out if kept at zero. If we explicitly set it to zero I
think we should also set all the other fields that way (DSTRD, NSSRS,
etc.).


Klaus

Re: [Qemu-devel] [PATCH] nvme: do not advertise support for unsupported arbitration mechanism

Posted by Max Reitz 4 years, 10 months ago

On 17.06.19 08:54, Klaus Birkelund wrote:
> On Fri, Jun 14, 2019 at 10:39:27PM +0200, Max Reitz wrote:
>> On 06.06.19 11:25, Klaus Birkelund Jensen wrote:
>>> The device mistakenly reports that the Weighted Round Robin with Urgent
>>> Priority Class arbitration mechanism is supported.
>>>
>>> It is not.
>>
>> I believe you based on the fact that there is no “weight” or “priority”
>> anywhere in nvme.c, and that it does not evaluate the Arbitration
>> Mechanism Selected field.
>>
> 
> Not sure if you want me to change the commit message? Feel free to
> change it if you want to ;)

Oh, no, no.  It’s just that I have no idea how the NVMe interface works
(well, I did download the spec then, but...), so this was basically just
my excuse for “I can review this!!”.

>>> Signed-off-by: Klaus Birkelund Jensen <klaus.jensen@cnexlabs.com>
>>> ---
>>>  hw/block/nvme.c | 1 -
>>>  1 file changed, 1 deletion(-)
>>>
>>> diff --git a/hw/block/nvme.c b/hw/block/nvme.c
>>> index 30e50f7a3853..415b4641d6b4 100644
>>> --- a/hw/block/nvme.c
>>> +++ b/hw/block/nvme.c
>>> @@ -1383,7 +1383,6 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
>>>      n->bar.cap = 0;
>>>      NVME_CAP_SET_MQES(n->bar.cap, 0x7ff);
>>>      NVME_CAP_SET_CQR(n->bar.cap, 1);
>>> -    NVME_CAP_SET_AMS(n->bar.cap, 1);
>>
>> I suppose the better way would be to pass 0, so it is more explicit, I
>> think.
>>
>> (Just removing it looks like it may have just been forgotten.)
>>
> 
> Not explicitly setting it to zero aligns with how the other fields in
> CAP are also left out if kept at zero. If we explicitly set it to zero I
> think we should also set all the other fields that way (DSTRD, NSSRS,
> etc.).

OK then.

Thanks, applied to my block branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block

Max