[LLava] Fix stats for C++ runner

Before:

I 00:00:28.414816 executorch:stats.h:84]        Prompt Tokens: 616    Generated Tokens: 33
I 00:00:28.414826 executorch:stats.h:90]        Model Load Time:                9.244000 (seconds)
I 00:00:28.414835 executorch:stats.h:100]       Total inference time:           0.000000 (seconds)               Rate:  inf (tokens/second)
I 00:00:28.414838 executorch:stats.h:108]               Prompt evaluation:      0.000000 (seconds)               Rate:  inf (tokens/second)
I 00:00:28.414839 executorch:stats.h:119]               Generated 33 tokens:    0.000000 (seconds)               Rate:  inf (tokens/second)
I 00:00:28.414841 executorch:stats.h:127]       Time to first generated token:  0.000000 (seconds)
I 00:00:28.414842 executorch:stats.h:134]       Sampling time over 649 tokens:  0.002000 (seconds)

With real image on M1:

I 00:00:34.231017 executorch:stats.h:84]        Prompt Tokens: 616    Generated Tokens: 33
I 00:00:34.231028 executorch:stats.h:90]        Model Load Time:                9.108000 (seconds)
I 00:00:34.231038 executorch:stats.h:100]       Total inference time:           25.103000 (seconds)              Rate:  1.314584 (tokens/second)
I 00:00:34.231040 executorch:stats.h:108]               Prompt evaluation:      11.544000 (seconds)              Rate:  53.361053 (tokens/second)
I 00:00:34.231042 executorch:stats.h:119]               Generated 33 tokens:    13.559000 (seconds)              Rate:  2.433808 (tokens/second)
I 00:00:34.231043 executorch:stats.h:127]       Time to first generated token:  11.544000 (seconds)
I 00:00:34.231045 executorch:stats.h:134]       Sampling time over 649 tokens:  0.000000 (seconds)

With bogus image (same dims) on Android S23:

I 00:00:34.649120 executorch:stats.h:84]        Prompt Tokens: 616    Generated Tokens: 33
I 00:00:34.649128 executorch:stats.h:90]        Model Load Time:                12.337000 (seconds)
I 00:00:34.649169 executorch:stats.h:100]       Total inference time:           22.301000 (seconds)              Rate:  1.479754 (tokens/second)
I 00:00:34.649174 executorch:stats.h:108]               Prompt evaluation:      17.964000 (seconds)              Rate:  34.290804 (tokens/second)
I 00:00:34.649179 executorch:stats.h:119]               Generated 33 tokens:    4.337000 (seconds)               Rate:  7.608946 (tokens/second)
I 00:00:34.649183 executorch:stats.h:127]       Time to first generated token:  17.964000 (seconds)
I 00:00:34.649186 executorch:stats.h:134]       Sampling time over 649 tokens:  0.001000 (seconds)

Author: digantdesai

examples/models/llava/runner/llava_runner.cpp

@@ -105,6 +105,8 @@ Error LlavaRunner::generate_from_pos(
 
   uint64_t prefill_next_token =
       ET_UNWRAP(prefill_prompt(prompt, start_pos, /*bos=*/0, /*eos*/ 0));
+  stats_.first_token_ms = util::time_in_ms();
+  stats_.prompt_eval_end_ms = util::time_in_ms();
   stats_.num_prompt_tokens = start_pos;
 
   // Generate tokens
@@ -113,7 +115,6 @@ Error LlavaRunner::generate_from_pos(
 
   // Bookkeeping
   stats_.num_generated_tokens = num_generated_tokens;
-  ::executorch::llm::print_report(stats_);
   if (stats_callback) {
     stats_callback(stats_);
   }
@@ -147,6 +148,7 @@ Error LlavaRunner::generate(
       };
 
   int64_t pos = 0;
+  stats_.inference_start_ms = util::time_in_ms();
 
   // prefill preset prompt
   prefill_prompt(kPresetPrompt, pos, /*bos=*/1, /*eos*/ 0);
@@ -160,8 +162,11 @@ Error LlavaRunner::generate(
       util::get_rss_bytes() / 1024.0 / 1024.0);
 
   // Generate tokens
-  Error err =
-      generate_from_pos(prompt, seq_len, pos, wrapped_callback, stats_callback);
+  Error err = generate_from_pos(
+      prompt, seq_len, pos, wrapped_callback, stats_callback);
+      
+  stats_.inference_end_ms = util::time_in_ms();
+  ::executorch::llm::print_report(stats_);
 
   ET_LOG(
       Info,