On Mon, Apr 15, 2024 at 6:25 AM Masami Hiramatsu (Google)
<mhiramat@xxxxxxxxxx> wrote:
>
> From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
>
> Skip recording calltime and rettime if the fgraph_ops does not need it.
> This is a kind of performance optimization for fprobe. Since the fprobe
> user does not use these entries, recording timestamp in fgraph is just
> a overhead (e.g. eBPF, ftrace). So introduce the skip_timestamp flag,
> and all fgraph_ops sets this flag, skip recording calltime and rettime.
>
> Suggested-by: Jiri Olsa <olsajiri@xxxxxxxxx>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> ---
> Changes in v9:
> - Newly added.
> ---
> include/linux/ftrace.h | 2 ++
> kernel/trace/fgraph.c | 46 +++++++++++++++++++++++++++++++++++++++-------
> kernel/trace/fprobe.c | 1 +
> 3 files changed, 42 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index d845a80a3d56..06fc7cbef897 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -1156,6 +1156,8 @@ struct fgraph_ops {
> struct ftrace_ops ops; /* for the hash lists */
> void *private;
> int idx;
> + /* If skip_timestamp is true, this does not record timestamps. */
> + bool skip_timestamp;
> };
>
> void *fgraph_reserve_data(int idx, int size_bytes);
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 7556fbbae323..a5722537bb79 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -131,6 +131,7 @@ DEFINE_STATIC_KEY_FALSE(kill_ftrace_graph);
> int ftrace_graph_active;
>
> static struct fgraph_ops *fgraph_array[FGRAPH_ARRAY_SIZE];
> +static bool fgraph_skip_timestamp;
>
> /* LRU index table for fgraph_array */
> static int fgraph_lru_table[FGRAPH_ARRAY_SIZE];
> @@ -475,7 +476,7 @@ void ftrace_graph_stop(void)
> static int
> ftrace_push_return_trace(unsigned long ret, unsigned long func,
> unsigned long frame_pointer, unsigned long *retp,
> - int fgraph_idx)
> + int fgraph_idx, bool skip_ts)
> {
> struct ftrace_ret_stack *ret_stack;
> unsigned long long calltime;
> @@ -498,8 +499,12 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func,
> ret_stack = get_ret_stack(current, current->curr_ret_stack, &index);
> if (ret_stack && ret_stack->func == func &&
> get_fgraph_type(current, index + FGRAPH_RET_INDEX) == FGRAPH_TYPE_BITMAP &&
> - !is_fgraph_index_set(current, index + FGRAPH_RET_INDEX, fgraph_idx))
> + !is_fgraph_index_set(current, index + FGRAPH_RET_INDEX, fgraph_idx)) {
> + /* If previous one skips calltime, update it. */
> + if (!skip_ts && !ret_stack->calltime)
> + ret_stack->calltime = trace_clock_local();
> return index + FGRAPH_RET_INDEX;
> + }
>
> val = (FGRAPH_TYPE_RESERVED << FGRAPH_TYPE_SHIFT) | FGRAPH_RET_INDEX;
>
> @@ -517,7 +522,10 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func,
> return -EBUSY;
> }
>
> - calltime = trace_clock_local();
> + if (skip_ts)
would it be ok to add likely() here to keep the least-overhead code path linear?
> + calltime = 0LL;
> + else
> + calltime = trace_clock_local();
>
> index = READ_ONCE(current->curr_ret_stack);
> ret_stack = RET_STACK(current, index);
> @@ -601,7 +609,8 @@ int function_graph_enter_regs(unsigned long ret, unsigned long func,
> trace.func = func;
> trace.depth = ++current->curr_ret_depth;
>
> - index = ftrace_push_return_trace(ret, func, frame_pointer, retp, 0);
> + index = ftrace_push_return_trace(ret, func, frame_pointer, retp, 0,
> + fgraph_skip_timestamp);
> if (index < 0)
> goto out;
>
> @@ -654,7 +663,8 @@ int function_graph_enter_ops(unsigned long ret, unsigned long func,
> return -ENODEV;
>
> /* Use start for the distance to ret_stack (skipping over reserve) */
> - index = ftrace_push_return_trace(ret, func, frame_pointer, retp, gops->idx);
> + index = ftrace_push_return_trace(ret, func, frame_pointer, retp, gops->idx,
> + gops->skip_timestamp);
> if (index < 0)
> return index;
> type = get_fgraph_type(current, index);
> @@ -732,6 +742,7 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
> *ret = ret_stack->ret;
> trace->func = ret_stack->func;
> trace->calltime = ret_stack->calltime;
> + trace->rettime = 0;
> trace->overrun = atomic_read(¤t->trace_overrun);
> trace->depth = current->curr_ret_depth;
> /*
> @@ -792,7 +803,6 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, unsigned long frame_pointe
> return (unsigned long)panic;
> }
>
> - trace.rettime = trace_clock_local();
> if (fregs)
> ftrace_regs_set_instruction_pointer(fregs, ret);
>
> @@ -808,6 +818,8 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, unsigned long frame_pointe
> continue;
> if (gops == &fgraph_stub)
> continue;
> + if (!trace.rettime && !gops->skip_timestamp)
In addition to the above, do you mind adding unlikely() here as well?
> + trace.rettime = trace_clock_local();
>
> gops->retfunc(&trace, gops, fregs);
> }
[...]
