Re: [PATCH 3/4] drm/amd/display: Add ref count control for FPU utilization

Am 31.03.21 um 14:25 schrieb Rodrigo Siqueira:

DC invokes DC_FPU_START/END in multiple parts of the code; this can create a situation where we invoke this FPU operation in a nested way. For avoiding this situation, this commit adds a mechanism where dc_fpu_begin/end manages the access to kernel_fpu_begin/end.

In general please name this "recursion" control instead of "ref count". Let's call the child by it's name :)

Signed-off-by: Rodrigo Siqueira Rodrigo.Siqueira@amd.com Acked-by: Rodrigo Siqueira Rodrigo.Siqueira@amd.com

---

.../amd/display/amdgpu_dm/amdgpu_dm_trace.h | 13 ++++--- .../gpu/drm/amd/display/amdgpu_dm/dc_fpu.c | 34 ++++++++++++++++--- drivers/gpu/drm/amd/display/dc/dc_trace.h | 4 +-- 3 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_trace.h b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_trace.h index 230bb12c405e..cd4f0d3f37fb 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_trace.h +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_trace.h @@ -638,23 +638,26 @@ TRACE_EVENT(amdgpu_refresh_rate_track, );

TRACE_EVENT(dcn_fpu,

•    TP_PROTO(bool begin, const char *function, const int line),
  

•    TP_ARGS(begin, function, line),
  

•    TP_PROTO(bool begin, const char *function, const int line, const int ref_count),
  

•    TP_ARGS(begin, function, line, ref_count),
  
   TP_STRUCT__entry(
       __field(bool, begin)
       __field(const char *, function)
       __field(int, line)
  

• 	     __field(int, ref_count)
  

  ), TP_fast_assign( __entry->begin = begin; __entry->function = function; __entry->line = line;

• 	   __entry->ref_count = ref_count;
  

  ),

•    TP_printk("%s()+%d: %s",
  

•    TP_printk("%s: ref_count: %d: %s()+%d:",
  

•       __entry->begin ? "begin" : "end",
  

•       __entry->ref_count,
   __entry->function,
  

•       __entry->line,
  

•       __entry->begin ? "begin" : "end"
  

•       __entry->line
  

  ) );

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c index ff34007509de..5dcefe193523 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c @@ -28,6 +28,19 @@

#include <asm/fpu/api.h>

+/**

• • DOC: Overview
• • DC core uses FPU operations in multiple parts of the code, which requires a
• • more specialized way to manage these areas' entrance. To fulfill this
• • requirement, we created some wrapper functions that encapsulate
• • kernel_fpu_begin/end to better fit our need in the display component. In
• • summary, in this file, you can find functions related to FPU operation
• • management.
• */

+static DEFINE_PER_CPU(atomic_t, fpu_ref);

• /**
  • dc_fpu_begin - Enables FPU protection
  • @function_name: A string containing the function name for debug purposes

@@ -40,8 +53,14 @@ */ void dc_fpu_begin(const char *function_name, const int line) {

• TRACE_DCN_FPU(true, function_name, line);
• kernel_fpu_begin();

• int ret;
• atomic_t *local_fpu_ref = this_cpu_ptr(&fpu_ref);
• ret = atomic_inc_return(local_fpu_ref);

You need to disable preemption for this or otherwise it can be that you schedule to another process.

Regards, Christian.

• TRACE_DCN_FPU(true, function_name, line, ret);

• if (ret == 1)

• kernel_fpu_begin();
  

  }

  /**

@@ -56,6 +75,13 @@ void dc_fpu_begin(const char *function_name, const int line) */ void dc_fpu_end(const char *function_name, const int line) {

• TRACE_DCN_FPU(false, function_name, line);
• kernel_fpu_end();

• int ret;
• atomic_t *local_fpu_ref = this_cpu_ptr(&fpu_ref);
• ret = atomic_dec_return(local_fpu_ref);
• TRACE_DCN_FPU(false, function_name, line, ret);
• if (!ret)

• kernel_fpu_end();
  

  }

diff --git a/drivers/gpu/drm/amd/display/dc/dc_trace.h b/drivers/gpu/drm/amd/display/dc/dc_trace.h index d598ba697e45..c711797e5c9e 100644 --- a/drivers/gpu/drm/amd/display/dc/dc_trace.h +++ b/drivers/gpu/drm/amd/display/dc/dc_trace.h @@ -38,5 +38,5 @@ #define TRACE_DCN_CLOCK_STATE(dcn_clocks) \ trace_amdgpu_dm_dc_clocks_state(dcn_clocks)

-#define TRACE_DCN_FPU(begin, function, line) \

• trace_dcn_fpu(begin, function, line)

+#define TRACE_DCN_FPU(begin, function, line, ref_count) \

• trace_dcn_fpu(begin, function, line, ref_count)