[PATCH] drm/i915/gvt: implement per-vm mmio switching optimization

[Du, Changbin]

On Tue, May 02, 2017 at 12:53:28AM -0700, Dong, Chuanxiao wrote:
> 
> 
> > -----Original Message-----
> > From: intel-gvt-dev [mailto:intel-gvt-dev-bounces at lists.freedesktop.org] On
> > Behalf Of changbin.du at gmail.com
> > Sent: Tuesday, May 2, 2017 12:52 PM
> > To: intel-gvt-dev at lists.freedesktop.org
> > Cc: Du, Changbin <changbin.du at intel.com>; Du at freedesktop.org
> > Subject: [PATCH] drm/i915/gvt: implement per-vm mmio switching
> > optimization
> > 
> > From: Changbin Du <changbin.du at intel.com>
> > 
> > Commit ab9da627906a ("drm/i915: make context status notifier head be per
> > engine") gives us a chance to inspect every single request. Then we can
> > eliminate unnecessary mmio switching for same vGPU. We only need mmio
> > switching for different VMs (including host).
> > 
> > This patch introduced a new general API intel_gvt_switch_mmio() to replace
> > the old intel_gvt_load/restore_render_mmio(). This function save the last
> > ring id internally which will be used for next switch.
> > 
> > This optimization is very useful if only one guest has plenty of workloads and
> > the host is mostly idle. The best case is no mmio switching will happen.
> > 
> > Signed-off-by: Changbin Du <changbin.du at intel.com>
> > Signed-off-by: Du, Changbin <changbin.du at intel.com>
> > ---
> >  drivers/gpu/drm/i915/gvt/render.c    | 39
> > ++++++++++++++++++++++++++++++++++--
> >  drivers/gpu/drm/i915/gvt/render.h    |  4 ++--
> >  drivers/gpu/drm/i915/gvt/scheduler.c | 29 ++++++++++++++++++++-------
> > drivers/gpu/drm/i915/gvt/scheduler.h |  2 ++
> >  4 files changed, 63 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gvt/render.c
> > b/drivers/gpu/drm/i915/gvt/render.c
> > index c6e7972..260ef83 100644
> > --- a/drivers/gpu/drm/i915/gvt/render.c
> > +++ b/drivers/gpu/drm/i915/gvt/render.c
> > @@ -260,7 +260,7 @@ static void restore_mocs(struct intel_vgpu *vgpu, int
> > ring_id)
> > 
> >  #define CTX_CONTEXT_CONTROL_VAL	0x03
> > 
> > -void intel_gvt_load_render_mmio(struct intel_vgpu *vgpu, int ring_id)
> > +static void switch_mmio_to_vgpu(struct intel_vgpu *vgpu, int ring_id)
> 
> As it is per-vm switching, is it really OK to only save/restore the mmio according to the specific ring instead of all the rings? As after switch to VGPU, other rings may also be used by VGPU.
>
Seems this aways is our defaut policy so far. We only switch the ring which will
be used, why switch other rings?


> >  {
> >  	struct drm_i915_private *dev_priv = vgpu->gvt->dev_priv;
> >  	struct render_mmio *mmio;
> > @@ -312,7 +312,7 @@ void intel_gvt_load_render_mmio(struct intel_vgpu
> > *vgpu, int ring_id)
> >  	handle_tlb_pending_event(vgpu, ring_id);  }
> > 
> > -void intel_gvt_restore_render_mmio(struct intel_vgpu *vgpu, int ring_id)
> > +static void switch_mmio_to_host(struct intel_vgpu *vgpu, int ring_id)
> 
> The same concern as the above.
> 
> Thanks
> Chuanxiao
> 

-- 
Thanks,
Changbin Du
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