How gpu requests are trapped by kvmgt ?

[Adel Belkhiri]

The number of "i915_gem_request_add" events (which indicate that a request
is added to the i915 queue) in the VM is bigger than the number of the same
event in the Host. The difference between the two numbers depends on the
frequency of sending requests to the gpu inside the VM.

To understand this behavior, I checked the function "execlists_dequeue" (in
the file intel_lrc.c) in the VM and found that whenever there are many
requests in the queue, to be submitted to the gpu, KVMGT is notified just
once through "execlists_context_status_change".


Le ven. 27 oct. 2017 à 01:05, Tian, Kevin <kevin.tian at intel.com> a écrit :

> Do you have more detail info where you actually add trace, and the exact
> number difference?
>
>
>
> *From:* Adel Belkhiri [mailto:adel.belkhiri at gmail.com]
> *Sent:* Friday, October 27, 2017 7:37 AM
> *To:* Tian, Kevin <kevin.tian at intel.com>
> *Cc:* intel-gvt-dev at lists.freedesktop.org
> *Subject:* Re: How gpu requests are trapped by kvmgt ?
>
>
>
> Thank you for your replay,
>
> What I wanted to say is that I found that the number of requests sent by
> the VM to the vgpu is different from the number of requests received by
> KVMGT. I used Ftrace to do the count.  I think the i915 driver of the VM
> sometimes combine multiple requests in just one request sent to KVMGT.
>
> Am I wrong ?
>
>
>
>
>
> Le mer. 25 oct. 2017 à 22:47, Tian, Kevin <kevin.tian at intel.com> a écrit :
>
> it’s decided by KVMGT. the real recipe is EPT, which is a CPU hw
> virtualization feature to decide which access in VM is trapped or not.
>
>
>
> *From:* intel-gvt-dev [mailto:intel-gvt-dev-bounces at lists.freedesktop.org]
> *On Behalf Of *Adel Belkhiri
> *Sent:* Wednesday, October 25, 2017 11:06 PM
> *To:* intel-gvt-dev at lists.freedesktop.org
> *Subject:* How gpu requests are trapped by kvmgt ?
>
>
>
> Hi everybody,
>
> I have a question about the implementation of KVMGT. According to the
> documentation, the virtual machine, may send some requests to the gpu
> directly (Pass-through) and forward some other requests to the KVMGT
> module.
>
> I read the code of KVMGT but i didn't understand how requests are being
> sent directly to the gpu ? and who decide which request to be directly sent
> to the gpu or to be trapped by kvmgt ? Is it the graphics card driver of
> the VM (i915) or KVMGT ?
>
> Thanks a lot for your help.
>
> Yours.
>
>
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