Re: [PATCH v3] drm/i915: Speed up DMC firmware loading

David Weinehall
2017-09-04T19:25:40Z

On Mon, Sep 04, 2017 at 08:15:57PM +0100, Chris Wilson wrote:
> Quoting Chris Wilson (2017-09-04 20:14:32)
> > Quoting David Weinehall (2017-09-04 20:08:06)
> > > 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...
> > >
> > > 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..28ea24932ef1 100644
> > > --- a/drivers/gpu/drm/i915/intel_csr.c
> > > +++ b/drivers/gpu/drm/i915/intel_csr.c
> > > @@ -240,6 +240,7 @@ void intel_csr_load_program(struct drm_i915_private *dev_priv)
> > > {
> > > u32 *payload = dev_priv->csr.dmc_payload;
> > > uint32_t i, fw_size;
> > > + unsigned long flags;
> > >
> > > if (!HAS_CSR(dev_priv)) {
> > > DRM_ERROR("No CSR support available for this platform\n");
> > > @@ -252,8 +253,13 @@ 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);
> > > + spin_lock_irqsave(&dev_priv->uncore.lock, flags);
> > > +
> > > for (i = 0; i < fw_size; i++)
> > > - I915_WRITE(CSR_PROGRAM(i), payload[i]);
> > > + I915_WRITE_FW(CSR_PROGRAM(i), payload[i]);
> > > +
> > > + spin_unlock_irqrestore(&dev_priv->uncore.lock, flags);
> >
> > Still would like to see the version without the uncore.lock. Afaict,
> > there isn't a requirement here -- unless you are serialising between
> > multiple users (concurrent intel_csr_load_program?) of CSR_PROGRAM.
>
> You may also want to consider a preempt_disable around this block as
> well, the argument being that we want the writes tightly grouped.
> -Chris

OK, I'll spin a non-spinning v4 tomorrow :)

Kind regards, David