Currently, the additional information of a branch entry is stored in a u64 space. With more and more information added, the space is running out. For example, the information of occurrences of events will be added for each branch. Two places were suggested to append the counters. https://lore.kernel.org/lkml/20230802215814.GH231007@hirez.programming.kicks-ass.net/ One place is right after the flags of each branch entry. It changes the existing struct perf_branch_entry. The later ARCH specific implementation has to be really careful to consistently pick the right struct. The other place is right after the entire struct perf_branch_stack. The disadvantage is that the pointer of the extra space has to be recorded. The common interface perf_sample_save_brstack() has to be updated. The latter is much straightforward, and should be easily understood and maintained. It is implemented in the patch. Add a new branch sample type, PERF_SAMPLE_BRANCH_COUNTERS, to indicate the event which is recorded in the branch info. The "u64 counters" may store the occurrences of several events. The information regarding the number of events/counters and the width of each counter should be exposed via sysfs as a reference for the perf tool. Define the branch_counter_nr and branch_counter_width ABI here. The support will be implemented later in the Intel-specific patch.
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| @@ -204,6 +204,8 @@ enum perf_branch_sample_type_shift { · 203 unmodified lines | ||
| 204 | 204 | |
| 205 | 205 | PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT = 18, /* save privilege mode */ |
| 206 | 206 | |
| 207 | + PERF_SAMPLE_BRANCH_COUNTERS_SHIFT = 19, /* save occurrences of events on a branch */ | |
| 208 | + | |
| 207 | 209 | PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */ |
| 208 | 210 | }; |
| 209 | 211 | |
| @@ -235,6 +237,8 @@ enum perf_branch_sample_type { · 25 unmodified lines | ||
| 235 | 237 | |
| 236 | 238 | PERF_SAMPLE_BRANCH_PRIV_SAVE = 1U << PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT, |
| 237 | 239 | |
| 240 | + PERF_SAMPLE_BRANCH_COUNTERS = 1U << PERF_SAMPLE_BRANCH_COUNTERS_SHIFT, | |
| 241 | + | |
| 238 | 242 | PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT, |
| 239 | 243 | }; |
| 240 | 244 | |
| @@ -982,6 +986,12 @@ enum perf_event_type { · 741 unmodified lines | ||
| 982 | 986 | * { u64 nr; |
| 983 | 987 | * { u64 hw_idx; } && PERF_SAMPLE_BRANCH_HW_INDEX |
| 984 | 988 | * { u64 from, to, flags } lbr[nr]; |
| 989 | + * # | |
| 990 | + * # The format of the counters is decided by the | |
| 991 | + * # "branch_counter_nr" and "branch_counter_width", | |
| 992 | + * # which are defined in the ABI. | |
| 993 | + * # | |
| 994 | + * { u64 counters; } cntr[nr] && PERF_SAMPLE_BRANCH_COUNTERS | |
| 985 | 995 | * } && PERF_SAMPLE_BRANCH_STACK |
| 986 | 996 | * |
| 987 | 997 | * { u64 abi; # enum perf_sample_regs_abi |