Re: [PATCH v9 3/9] perf c2c: add column rendering for function view

[Ian Rogers]

On Mon, Aug 17, 2026 at 2:40 AM Jiebin Sun <jiebin.sun@xxxxxxxxx> wrote:
>
> Add renderers for the function view's Cycles %, Store count, and
> hierarchy identity columns. The identity column renders the read-side
> function, contending writer, or cacheline, with indentation for the
> hierarchy level. Also add width and header helpers, estimated-cycle
> calculation, comparators, and the dimension table that ties them together.
>
> Clamp the identity renderer's returned length to its local buffer before
> using it for pointer and padding calculations. This handles snprintf-style
> would-have-been lengths without changing normal output.
>
> The next patch connects these dimensions to the view's HPP lists, so the
> symbols used only there are temporarily marked __maybe_unused.
>
> Signed-off-by: Jiebin Sun <jiebin.sun@xxxxxxxxx>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> Cc: Ian Rogers <irogers@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: James Clark <james.clark@xxxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Thomas Falcon <thomas.falcon@xxxxxxxxx>
> Reviewed-by: Tianyou Li <tianyou.li@xxxxxxxxx>
> Reviewed-by: Wangyang Guo <wangyang.guo@xxxxxxxxx>

Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>

> ---
>  tools/perf/util/c2c-function.c | 353 +++++++++++++++++++++++++++++++++
>  1 file changed, 353 insertions(+)
>
> diff --git a/tools/perf/util/c2c-function.c b/tools/perf/util/c2c-function.c
> index ca82425a28dc..7fce415c0f07 100644
> --- a/tools/perf/util/c2c-function.c
> +++ b/tools/perf/util/c2c-function.c
> @@ -64,3 +64,356 @@ static inline __maybe_unused u64 hist_entry__iaddr(struct hist_entry *he)
>                 return mem_info__iaddr(he->mem_info)->addr;
>         return he->ip;
>  }
> +
> +/*
> + * Hierarchy levels (by depth): L1 = read-side function, L2 = the writing
> + * function it contends with, L3 = the specific shared cacheline.
> + */
> +static inline bool hist_entry__is_cacheline(struct hist_entry *he)

nit: I think the inline here is to make things compile/link in the
partial state. In general it shouldn't be necessary to have "inline"
in a .c file.

Thanks,
Ian

> +{
> +       return he->parent_he && he->parent_he->parent_he;       /* level 3: cacheline */
> +}
> +
> +/* Spaces of indent per hierarchy level, like the normal report view. */
> +#define C2C_FUNC_INDENT 2
> +
> +/* Width of the folded-sign prefix ("%c ") each identity cell emits. */
> +#define C2C_FUNC_FOLD_WIDTH 2
> +
> +/*
> + * Write he->depth levels of leading indentation into @buf, so lower-level
> + * entries are visually nested under their parent. Returns bytes written.
> + */
> +static int hist_entry__indent(struct hist_entry *he, char *buf, size_t size)
> +{
> +       int indent = he->depth * C2C_FUNC_INDENT;
> +
> +       if (indent <= 0 || (size_t)indent >= size)
> +               return 0;
> +
> +       return scnprintf(buf, size, "%*s", indent, "");
> +}
> +
> +static int symbol_width(struct hists *hists, struct sort_entry *se)
> +{
> +       int width = hists__col_len(hists, se->se_width_idx);
> +
> +       /*
> +        * Cap long symbol names as the cacheline view does. The stored column
> +        * length is grown up front to fit the deepest, longest identity cell
> +        * (including a level-3 cacheline address), so this cap never shrinks the
> +        * column below what the cacheline address needs.
> +        */
> +       if (!c2c_ext.symbol_full && width > SYMBOL_WIDTH)
> +               width = SYMBOL_WIDTH;
> +
> +       return width;
> +}
> +
> +static struct c2c_dimension dim_symbol_view;
> +
> +/*
> + * c2c_width - Calculate width for a C2C column in function view
> + */
> +static int c2c_width(struct perf_hpp_fmt *fmt,
> +                    struct perf_hpp *hpp __maybe_unused,
> +                    struct hists *hists)
> +{
> +       struct c2c_fmt *c2c_fmt;
> +       struct c2c_dimension *dim;
> +
> +       c2c_fmt = container_of(fmt, struct c2c_fmt, fmt);
> +       dim = c2c_fmt->dim;
> +
> +       if (dim == &dim_symbol_view)
> +               return symbol_width(hists, dim->se);
> +
> +       return dim->se ? hists__col_len(hists, dim->se->se_width_idx) :
> +                        dim->width;
> +}
> +
> +static int __maybe_unused c2c_header(struct perf_hpp_fmt *fmt, struct perf_hpp *hpp,
> +                                    struct hists *hists, int line, int *span)
> +{
> +       struct c2c_fmt *c2c_fmt;
> +       struct c2c_dimension *dim;
> +       const char *text = NULL;
> +       int width = c2c_width(fmt, hpp, hists);
> +
> +       c2c_fmt = container_of(fmt, struct c2c_fmt, fmt);
> +       dim = c2c_fmt->dim;
> +
> +       if (dim->se) {
> +               text = dim->header.line[line].text;
> +               /* Use the last line from sort_entry if not defined. */
> +               if (!text && line == hists->hpp_list->nr_header_lines - 1)
> +                       text = dim->se->se_header;
> +       } else {
> +               text = dim->header.line[line].text;
> +
> +               if (span) {
> +                       if (*span) {
> +                               (*span)--;
> +                               return 0;
> +                       }
> +
> +                       *span = dim->header.line[line].span;
> +               }
> +       }
> +
> +       if (!text)
> +               text = "";
> +
> +       return scnprintf(hpp->buf, hpp->size, "%*s", width, text);
> +}
> +
> +/*
> + * Return the estimated total cycles for a c2c_hist_entry
> + * (rmt_hitm + lcl_hitm + rmt_peer + lcl_peer + other loads).
> + */
> +static u64 c2c_hist_entry__cycles(struct c2c_hist_entry *c2c_he)
> +{
> +       struct compute_stats *cs = &c2c_he->cstats;
> +       double cycles = 0;
> +
> +       /*
> +        * compute_stats() in builtin-c2c.c routes each load sample into exactly
> +        * one cstats bucket (rmt_hitm, lcl_hitm, rmt_peer, lcl_peer or plain
> +        * load), so each bucket's cycle total is its mean times its own sample
> +        * count. Summing the per-bucket totals avoids both dropping peer-snoop
> +        * cycles and double counting a sample that carries several data-source
> +        * flags (e.g. Arm SPE sets HITM and PEER on the same load), which would
> +        * happen if the mean were multiplied by the non-exclusive stats counts.
> +        */
> +       cycles += avg_stats(&cs->rmt_hitm) * cs->rmt_hitm.n;
> +       cycles += avg_stats(&cs->lcl_hitm) * cs->lcl_hitm.n;
> +       cycles += avg_stats(&cs->rmt_peer) * cs->rmt_peer.n;
> +       cycles += avg_stats(&cs->lcl_peer) * cs->lcl_peer.n;
> +       cycles += avg_stats(&cs->load)     * cs->load.n;
> +
> +       return (u64)cycles;
> +}
> +
> +/* Sum c2c_hist_entry__cycles() across all level-1 entries. */
> +static u64 __maybe_unused c2c_ext__total_cycles(void)
> +{
> +       struct rb_node *nd;
> +       u64 total = 0;
> +
> +       for (nd = rb_first_cached(&c2c_ext.function_hists.hists.entries); nd;
> +            nd = rb_next(nd)) {
> +               struct c2c_hist_entry *c2c_he =
> +                       rb_entry(nd, struct c2c_hist_entry, he.rb_node);
> +
> +               total += c2c_hist_entry__cycles(c2c_he);
> +       }
> +       return total;
> +}
> +
> +/*
> + * Store count shown in the column: a level-3 cacheline leaf shows its parent
> + * level-2 writer's stores on that line, not all stores on the line. A level-2
> + * writer shows the sum across its level-3 cachelines. A level-1 reader shows
> + * the sum across all included writers on the cachelines it reads; this is not
> + * the reader function's own store count and is not additive across readers.
> + */
> +static u64 hist_entry__displayed_stores(struct hist_entry *he)
> +{
> +       struct c2c_hist_entry *c2c_he = container_of(he, struct c2c_hist_entry, he);
> +       struct rb_node *nd;
> +       u64 stores = 0;
> +
> +       /* Level-2/3 entries already aggregate the stores they represent. */
> +       if (he->parent_he)
> +               return c2c_he->stats.store;
> +
> +       for (nd = rb_first_cached(&he->hroot_out); nd; nd = rb_next(nd)) {
> +               struct c2c_hist_entry *child_c2c =
> +                       rb_entry(nd, struct c2c_hist_entry, he.rb_node);
> +               stores += child_c2c->stats.store;
> +       }
> +       return stores;
> +}
> +
> +static int
> +total_stores_entry(struct perf_hpp_fmt *fmt, struct perf_hpp *hpp,
> +                  struct hist_entry *he)
> +{
> +       int width = c2c_width(fmt, hpp, he->hists);
> +       u64 total = hist_entry__displayed_stores(he);
> +
> +       return scnprintf(hpp->buf, hpp->size, "%*" PRIu64, width, total);
> +}
> +
> +/*
> + * symbol_view_entry - Render the unified, indented identity column.
> + *
> + * All three levels share this single column so the hierarchy reads top-down
> + * with progressive indentation, like the normal report hierarchy view. It is
> + * a function-centric view with no dedicated code-address column. Verbose
> + * function rows can still include a representative address:
> + *   L1 read-side function: "- [k] cpupri_set"
> + *   L2 writing function:   "  - [k] pull_rt_task"
> + *   L3 shared cacheline:   "      0xff2d0082809da080"
> + */
> +static int
> +symbol_view_entry(struct perf_hpp_fmt *fmt, struct perf_hpp *hpp,
> +                 struct hist_entry *he)
> +{
> +       int width = c2c_width(fmt, hpp, he->hists);
> +       int text_width;
> +       int ret;
> +       char folded_sign;
> +
> +       ret = hist_entry__indent(he, hpp->buf, hpp->size);
> +
> +       folded_sign = he->has_children ? (he->unfolded ? '-' : '+') : ' ';
> +       ret += scnprintf(hpp->buf + ret, hpp->size - ret, "%c ", folded_sign);
> +
> +       text_width = width - ret;
> +       if (text_width <= 0)
> +               return ret;
> +
> +       if (hist_entry__is_cacheline(he)) {
> +               /* Level 3: the shared cacheline address. */
> +               u64 addr = he->mem_info ?
> +                       cl_address(mem_info__daddr(he->mem_info)->addr, chk_double_cl) : 0;
> +               char symbuf[32];
> +
> +               scnprintf(symbuf, sizeof(symbuf), "0x%" PRIx64, addr);
> +               ret += scnprintf(hpp->buf + ret, hpp->size - ret, "%-*.*s",
> +                                text_width, text_width, symbuf);
> +       } else {
> +               /* Level 1 and level 2 are both functions. */
> +               size_t cell_size;
> +               int len;
> +
> +               if ((size_t)ret >= hpp->size)
> +                       return ret;
> +
> +               cell_size = min_t(size_t, hpp->size - ret,
> +                                 (size_t)text_width + 1);
> +               len = sort_sym.se_snprintf(he, hpp->buf + ret, cell_size,
> +                                          text_width);
> +               /*
> +                * se_snprintf() accumulates repsep_snprintf() calls, which cap
> +                * their return at the remaining size - 1 rather than reporting
> +                * what the format would have needed, so len stays below
> +                * cell_size. Clamp anyway so ret cannot leave hpp->buf.
> +                */
> +               if (len < 0)
> +                       len = 0;
> +               else
> +                       len = min_t(size_t, len, cell_size - 1);
> +
> +               ret += len;
> +               if (len < text_width)
> +                       ret += scnprintf(hpp->buf + ret, hpp->size - ret, "%*s",
> +                                        text_width - len, "");
> +       }
> +
> +       return ret;
> +}
> +
> +/*
> + * cycles_percent_entry - Render cycles percentage column
> + */
> +static int
> +cycles_percent_entry(struct perf_hpp_fmt *fmt, struct perf_hpp *hpp,
> +                    struct hist_entry *he)
> +{
> +       struct c2c_hist_entry *c2c_he;
> +       int width = c2c_width(fmt, hpp, he->hists);
> +       u64 fn_cycles, total_cycles;
> +       char folded_sign;
> +       double pct;
> +       int ret, pct_width;
> +
> +       /* Hide Cycles Percent for child functions and cachelines. */
> +       if (he->parent_he)
> +               return scnprintf(hpp->buf, hpp->size, "%*s", width, "");
> +
> +       c2c_he = container_of(he, struct c2c_hist_entry, he);
> +       fn_cycles = c2c_hist_entry__cycles(c2c_he);
> +       /* Populated by build_function_view_hierarchy() once the L1 tree is built. */
> +       total_cycles = c2c_ext.total_cycles;
> +       pct = total_cycles > 0 ? (double)fn_cycles / total_cycles * 100.0 : 0.0;
> +
> +       /* Add folded sign only for level-1 entries */
> +       folded_sign = he->has_children ? (he->unfolded ? '-' : '+') : ' ';
> +       ret = scnprintf(hpp->buf, hpp->size, "%c ", folded_sign);
> +
> +       pct_width = width - ret;
> +       if (pct_width <= 0)
> +               return ret;
> +       ret += scnprintf(hpp->buf + ret, hpp->size - ret, "%*.2f%%", pct_width - 1, pct);
> +       return ret;
> +}
> +
> +/*
> + * cycles_percent_cmp - Comparison function for cycles percentage sorting
> + */
> +static int64_t
> +cycles_percent_cmp(struct perf_hpp_fmt *fmt __maybe_unused,
> +                  struct hist_entry *left, struct hist_entry *right)
> +{
> +       struct c2c_hist_entry *c2c_left = container_of(left, struct c2c_hist_entry, he);
> +       struct c2c_hist_entry *c2c_right = container_of(right, struct c2c_hist_entry, he);
> +       u64 cycles_left, cycles_right;
> +
> +       /* Cycles Percent is only shown for level-1 entries; others compare equal. */
> +       if (left->parent_he || right->parent_he)
> +               return 0;
> +
> +       cycles_left = c2c_hist_entry__cycles(c2c_left);
> +       cycles_right = c2c_hist_entry__cycles(c2c_right);
> +
> +       return (cycles_left > cycles_right) - (cycles_left < cycles_right);
> +}
> +
> +/*
> + * total_stores_cmp - Comparison function for total stores sorting
> + */
> +static int64_t
> +total_stores_cmp(struct perf_hpp_fmt *fmt __maybe_unused,
> +                struct hist_entry *left, struct hist_entry *right)
> +{
> +       u64 left_store = hist_entry__displayed_stores(left);
> +       u64 right_store = hist_entry__displayed_stores(right);
> +
> +       return (left_store > right_store) - (left_store < right_store);
> +}
> +
> +/*
> + * Function view dimensions
> + */
> +static struct c2c_dimension dim_cycles_percent = {
> +       .header         = HEADER_BOTH("Cycles", "%"),
> +       .name           = "cycles_percent",
> +       .cmp            = cycles_percent_cmp,
> +       .entry          = cycles_percent_entry,
> +       .width          = 9,
> +};
> +
> +static struct c2c_dimension dim_total_stores = {
> +       .header         = HEADER_BOTH("Store", "count"),
> +       .name           = "total_stores",
> +       .cmp            = total_stores_cmp,
> +       .entry          = total_stores_entry,
> +       .width          = 7,
> +};
> +
> +static struct c2c_dimension dim_symbol_view = {
> +       .header         = HEADER_LOW("Function / Contending function / Cacheline"),
> +       .name           = "symbol_view",
> +       .se             = &sort_sym,
> +       .entry          = symbol_view_entry,
> +       .width          = SYMBOL_WIDTH,
> +};
> +
> +static struct c2c_dimension *function_view_dimensions[] __maybe_unused = {
> +       &dim_cycles_percent,
> +       &dim_total_stores,
> +       &dim_symbol_view,
> +       NULL,
> +};
> --
> 2.52.0
>