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SubjectRe: [PATCH] perf ftrace: Factor regs retrieval for function tracer
On Thu, Dec 18, 2014 at 03:08:47PM +0100, Jiri Olsa wrote:
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index 6fa484de2ba1..54bffedd28b6 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -304,7 +304,7 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
> {
> struct ftrace_entry *entry;
> struct hlist_head *head;
> - struct pt_regs regs;
> + struct pt_regs **regsp, *regs = pt_regs;
> int rctx;
>
> head = this_cpu_ptr(event_function.perf_events);
> @@ -316,16 +316,24 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
>
> BUILD_BUG_ON(ENTRY_SIZE > PERF_MAX_TRACE_SIZE);
>
> - perf_fetch_caller_regs(&regs);
> + /*
> + * The ftrace_ops is registered with SAVE_REGS_IF_SUPPORTED,
> + * so if we got pt_regs defined, we don't need to retrieve
> + * regs buffer through perf_trace_buf_prepare.
> + */
> + regsp = pt_regs ? NULL : &regs;
>
> - entry = perf_trace_buf_prepare(ENTRY_SIZE, TRACE_FN, NULL, &rctx);
> + entry = perf_trace_buf_prepare(ENTRY_SIZE, TRACE_FN, regsp, &rctx);
> if (!entry)
> return;
>
> + if (regsp)
> + perf_fetch_caller_regs(regs);
> +


Would not something like:

struct pt_regs *regs;

entry = perf_trace_buf_prepare(ENTRY_SIZE, TRACE_FN, &regs, &rctx);
if (!pt_regs) {
perf_fetch_caller_regs(regs);
pt_regs = regs;
}

Be simpler?


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