[Intel-gfx] [RFC 03/10] drm/i915/gvt: context submission pvmmio optimization

[Zhang, Xiaolin]

On 09/27/2018 03:21 PM, Chris Wilson wrote:
> Quoting Xiaolin Zhang (2018-09-27 17:37:48)
>> It is performance optimization to reduce mmio trap numbers from 4 to
>> 1 durning ELSP porting writing (context submission).
>>
>> When context subission, to cache elsp_data[4] values in
>> the shared page, the last elsp_data[0] port writing will be trapped
>> to gvt for real context submission.
>>
>> Use PVMMIO_ELSP_SUBMIT to control this level of pvmmio optimization.
>> Signed-off-by: Xiaolin Zhang <xiaolin.zhang at intel.com>
>> ---
>>  drivers/gpu/drm/i915/i915_params.h |  2 +-
>>  drivers/gpu/drm/i915/intel_lrc.c   | 37 ++++++++++++++++++++++++++++++++++++-
>>  2 files changed, 37 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
>> index 0f6a38b..6c81c87 100644
>> --- a/drivers/gpu/drm/i915/i915_params.h
>> +++ b/drivers/gpu/drm/i915/i915_params.h
>> @@ -69,7 +69,7 @@
>>         param(bool, enable_dp_mst, true) \
>>         param(bool, enable_dpcd_backlight, false) \
>>         param(bool, enable_gvt, false) \
>> -       param(int, enable_pvmmio, 0)
>> +       param(int, enable_pvmmio, PVMMIO_ELSP_SUBMIT)
>>  
>>  #define MEMBER(T, member, ...) T member;
>>  struct i915_params {
>> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
>> index 4b28225..cdc713c 100644
>> --- a/drivers/gpu/drm/i915/intel_lrc.c
>> +++ b/drivers/gpu/drm/i915/intel_lrc.c
>> @@ -451,7 +451,12 @@ static void execlists_submit_ports(struct intel_engine_cs *engine)
>>  {
>>         struct intel_engine_execlists *execlists = &engine->execlists;
>>         struct execlist_port *port = execlists->port;
>> +       u32 __iomem *elsp =
>> +               engine->i915->regs + i915_mmio_reg_offset(RING_ELSP(engine));
>> +       u32 *elsp_data;
>>         unsigned int n;
>> +       u32 descs[4];
>> +       int i = 0;
>>  
>>         /*
>>          * We can skip acquiring intel_runtime_pm_get() here as it was taken
>> @@ -494,8 +499,24 @@ static void execlists_submit_ports(struct intel_engine_cs *engine)
>>                         GEM_BUG_ON(!n);
>>                         desc = 0;
>>                 }
>> +               if (PVMMIO_LEVEL_ENABLE(engine->i915, PVMMIO_ELSP_SUBMIT)) {
>> +                       GEM_BUG_ON(i >= 4);
>> +                       descs[i] = upper_32_bits(desc);
>> +                       descs[i + 1] = lower_32_bits(desc);
>> +                       i += 2;
>> +               } else {
>> +                       write_desc(execlists, desc, n);
>> +               }
>> +       }
>>  
>> -               write_desc(execlists, desc, n);
>> +       if (PVMMIO_LEVEL_ENABLE(engine->i915, PVMMIO_ELSP_SUBMIT)) {
>> +               spin_lock(&engine->i915->shared_page_lock);
>> +               elsp_data = engine->i915->shared_page->elsp_data;
>> +               *elsp_data = descs[0];
>> +               *(elsp_data + 1) = descs[1];
>> +               *(elsp_data + 2) = descs[2];
>> +               writel(descs[3], elsp);
>> +               spin_unlock(&engine->i915->shared_page_lock);
>>         }
>>  
>>         /* we need to manually load the submit queue */
>> @@ -538,11 +559,25 @@ static void inject_preempt_context(struct intel_engine_cs *engine)
>>         struct intel_engine_execlists *execlists = &engine->execlists;
>>         struct intel_context *ce =
>>                 to_intel_context(engine->i915->preempt_context, engine);
>> +       u32 __iomem *elsp =
>> +               engine->i915->regs + i915_mmio_reg_offset(RING_ELSP(engine));
>> +       u32 *elsp_data;
>>         unsigned int n;
>>  
>>         GEM_BUG_ON(execlists->preempt_complete_status !=
>>                    upper_32_bits(ce->lrc_desc));
>>  
>> +       if (PVMMIO_LEVEL_ENABLE(engine->i915, PVMMIO_ELSP_SUBMIT)) {
>> +               spin_lock(&engine->i915->shared_page_lock);
>> +               elsp_data = engine->i915->shared_page->elsp_data;
>> +               *elsp_data = 0;
>> +               *(elsp_data + 1) = 0;
>> +               *(elsp_data + 2) = upper_32_bits(ce->lrc_desc);
>> +               writel(lower_32_bits(ce->lrc_desc), elsp);
>> +               spin_unlock(&engine->i915->shared_page_lock);
>> +               return;
>> +       }
>> +
> Really?
> -Chris
in normal case,  write_desc will update port[0] & port[1] descriptor and
in total 4 mmio will be accessed and trapped.
in PVMMIO_ELSP_SUBMIT case,  cache descs[0] ~ descs[4] to elsp_data[4]
in shared_page, just use one mmio access
"writel(descs[3], elsp)" to trap to GVTg for workload submission and in
GVGT the desc[0]~desc[2] will be read from shared_page.
>