Re: [PATCH v4] drm/i915: Speed up DMC firmware loading

David Weinehall
2017-09-05T13:33:06Z

On Tue, Sep 05, 2017 at 02:25:36PM +0100, Chris Wilson wrote:
> Quoting David Weinehall (2017-09-05 14:10:50)
> > Currently we're doing:
> >
> > 1. acquire lock
> > 2. write word to hardware
> > 3. release lock
> > 4. repeat from 1
> >
> > to load the DMC firmware. Due to the cost of acquiring/releasing a lock,
> > and the size of the DMC firmware, this slows down DMC loading a lot.
> >
> > This patch simply acquires the lock, writes the entire firmware,
> > then releases the lock. Testing shows resume speedups
> > in the order of 10ms on platforms with DMC firmware (GEN9+).
> >
> > v2: Per feedback from Chris & Ville there's no need to do the whole
> > forcewake dance, so lose that bit (Chris, Ville)
> >
> > v3: Actually send the new version of the patch...
> >
> > v4: Don't acquire the uncore lock. Disable preempt. (Chris)
> >
> > Signed-off-by: David Weinehall <david.weinehall@linux.intel.com>
> > ---
> > drivers/gpu/drm/i915/intel_csr.c | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_csr.c b/drivers/gpu/drm/i915/intel_csr.c
> > index 965988f79a55..cdfb624eb82d 100644
> > --- a/drivers/gpu/drm/i915/intel_csr.c
> > +++ b/drivers/gpu/drm/i915/intel_csr.c
> > @@ -252,8 +252,14 @@ void intel_csr_load_program(struct drm_i915_private *dev_priv)
> > }
> >
> > fw_size = dev_priv->csr.dmc_fw_size;
> > + assert_rpm_wakelock_held(dev_priv);
> > +
> > + preempt_disable();
> > +
> > for (i = 0; i < fw_size; i++)
> > - I915_WRITE(CSR_PROGRAM(i), payload[i]);
> > + I915_WRITE_FW(CSR_PROGRAM(i), payload[i]);
> > +
> > + preempt_enable();
> >
> > for (i = 0; i < dev_priv->csr.mmio_count; i++) {
> > I915_WRITE(dev_priv->csr.mmioaddr[i],
>
> Looked into extending the coverage to the second loop?

The second loop didn't really show up in my benchmarks,
so I decided to minimise the changes.

The only other I915_WRITE() loops that show up when measuring
are the LUT loading; I'll fix those in a future patch.

Kind regards, David