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Message-ID: <20220714154212.4efb86c7@gandalf.local.home>
Date: Thu, 14 Jul 2022 15:42:12 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Dmitrii Dolgov <9erthalion6@...il.com>, peterz@...radead.org
Cc: linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
songliubraving@...com, mingo@...hat.com, mhiramat@...nel.org,
alexei.starovoitov@...il.com
Subject: Re: [PATCH v4 1/1] perf/kprobe: maxactive for fd-based kprobe
Peter,
Since this is mostly perf related, care to take it?
-- Steve
On Thu, 14 Jul 2022 21:34:03 +0200
Dmitrii Dolgov <9erthalion6@...il.com> wrote:
> From: Song Liu <songliubraving@...com>
>
> Enable specifying maxactive for fd based kretprobe. This will be useful
> for tracing tools like bcc and bpftrace (see for example discussion [1]).
> Use highest 4 bit (bit 59-63) to allow specifying maxactive by log2.
>
> The original patch [2] seems to be fallen through the cracks and wasn't
> applied. I've merely rebased the work done by Song Liu, verififed it
> still works, and modified to allow specifying maxactive by log2 per
> suggestion from the discussion thread.
>
> Note that changes in rethook implementation may render maxactive
> obsolete.
>
> [1]: https://github.com/iovisor/bpftrace/issues/835
> [2]: https://lore.kernel.org/all/20191007223111.1142454-1-songliubraving@fb.com/
>
> Signed-off-by: Song Liu <songliubraving@...com>
> Signed-off-by: Dmitrii Dolgov <9erthalion6@...il.com>
> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> Acked-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
> Previous discussion: https://lore.kernel.org/bpf/20220625152429.27539-1-9erthalion6@gmail.com/
>
> Resent with LKML in Cc instead of linux-perf-users, as it is a kernel
> change.
>
> Changes in v4:
> - Allow specifying maxactive by log2
>
> Changes in v3:
> - Set correct author
>
> Changes in v2:
> - Fix comment about number bits for the offset
>
> include/linux/trace_events.h | 3 ++-
> kernel/events/core.c | 20 ++++++++++++++++----
> kernel/trace/trace_event_perf.c | 5 +++--
> kernel/trace/trace_kprobe.c | 4 ++--
> kernel/trace/trace_probe.h | 2 +-
> 5 files changed, 24 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index e6e95a9f07a5..7ca453a73252 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -850,7 +850,8 @@ extern void perf_trace_destroy(struct perf_event *event);
> extern int perf_trace_add(struct perf_event *event, int flags);
> extern void perf_trace_del(struct perf_event *event, int flags);
> #ifdef CONFIG_KPROBE_EVENTS
> -extern int perf_kprobe_init(struct perf_event *event, bool is_retprobe);
> +extern int perf_kprobe_init(struct perf_event *event, bool is_retprobe,
> + int max_active);
> extern void perf_kprobe_destroy(struct perf_event *event);
> extern int bpf_get_kprobe_info(const struct perf_event *event,
> u32 *fd_type, const char **symbol,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 23bb19716ad3..184325ff2656 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9809,24 +9809,34 @@ static struct pmu perf_tracepoint = {
> * PERF_PROBE_CONFIG_IS_RETPROBE if set, create kretprobe/uretprobe
> * if not set, create kprobe/uprobe
> *
> - * The following values specify a reference counter (or semaphore in the
> - * terminology of tools like dtrace, systemtap, etc.) Userspace Statically
> - * Defined Tracepoints (USDT). Currently, we use 40 bit for the offset.
> + * PERF_UPROBE_REF_CTR_OFFSET_* specify a reference counter (or semaphore
> + * in the terminology of tools like dtrace, systemtap, etc.) Userspace
> + * Statically Defined Tracepoints (USDT). Currently, we use 32 bit for the
> + * offset.
> *
> * PERF_UPROBE_REF_CTR_OFFSET_BITS # of bits in config as th offset
> * PERF_UPROBE_REF_CTR_OFFSET_SHIFT # of bits to shift left
> + *
> + * PERF_KPROBE_MAX_ACTIVE_* defines log2 of max_active for kretprobe.
> + * KRETPROBE_MAXACTIVE_MAX is 4096. We allow 4095 here to save a bit.
> */
> enum perf_probe_config {
> PERF_PROBE_CONFIG_IS_RETPROBE = 1U << 0, /* [k,u]retprobe */
> PERF_UPROBE_REF_CTR_OFFSET_BITS = 32,
> PERF_UPROBE_REF_CTR_OFFSET_SHIFT = 64 - PERF_UPROBE_REF_CTR_OFFSET_BITS,
> + PERF_KPROBE_MAX_ACTIVE_BITS = 4,
> + PERF_KPROBE_MAX_ACTIVE_SHIFT = 64 - PERF_KPROBE_MAX_ACTIVE_BITS,
> };
>
> PMU_FORMAT_ATTR(retprobe, "config:0");
> #endif
>
> #ifdef CONFIG_KPROBE_EVENTS
> +/* max_active is specified by log2, to allow larger values if needed */
> +PMU_FORMAT_ATTR(max_active_log2, "config:59-63");
> +
> static struct attribute *kprobe_attrs[] = {
> + &format_attr_max_active_log2.attr,
> &format_attr_retprobe.attr,
> NULL,
> };
> @@ -9857,6 +9867,7 @@ static int perf_kprobe_event_init(struct perf_event *event)
> {
> int err;
> bool is_retprobe;
> + int max_active_log2;
>
> if (event->attr.type != perf_kprobe.type)
> return -ENOENT;
> @@ -9871,7 +9882,8 @@ static int perf_kprobe_event_init(struct perf_event *event)
> return -EOPNOTSUPP;
>
> is_retprobe = event->attr.config & PERF_PROBE_CONFIG_IS_RETPROBE;
> - err = perf_kprobe_init(event, is_retprobe);
> + max_active_log2 = event->attr.config >> PERF_KPROBE_MAX_ACTIVE_SHIFT;
> + err = perf_kprobe_init(event, is_retprobe, 1U << max_active_log2);
> if (err)
> return err;
>
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index a114549720d6..129000327809 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -245,7 +245,8 @@ void perf_trace_destroy(struct perf_event *p_event)
> }
>
> #ifdef CONFIG_KPROBE_EVENTS
> -int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe)
> +int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe,
> + int max_active)
> {
> int ret;
> char *func = NULL;
> @@ -271,7 +272,7 @@ int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe)
>
> tp_event = create_local_trace_kprobe(
> func, (void *)(unsigned long)(p_event->attr.kprobe_addr),
> - p_event->attr.probe_offset, is_retprobe);
> + p_event->attr.probe_offset, is_retprobe, max_active);
> if (IS_ERR(tp_event)) {
> ret = PTR_ERR(tp_event);
> goto out;
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 47cebef78532..3ad30cfce9c3 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1784,7 +1784,7 @@ static int unregister_kprobe_event(struct trace_kprobe *tk)
> /* create a trace_kprobe, but don't add it to global lists */
> struct trace_event_call *
> create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> - bool is_return)
> + bool is_return, int max_active)
> {
> enum probe_print_type ptype;
> struct trace_kprobe *tk;
> @@ -1799,7 +1799,7 @@ create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> event = func ? func : "DUMMY_EVENT";
>
> tk = alloc_trace_kprobe(KPROBE_EVENT_SYSTEM, event, (void *)addr, func,
> - offs, 0 /* maxactive */, 0 /* nargs */,
> + offs, max_active, 0 /* nargs */,
> is_return);
>
> if (IS_ERR(tk)) {
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index 92cc149af0fd..26fe21980793 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -376,7 +376,7 @@ extern int traceprobe_set_print_fmt(struct trace_probe *tp, enum probe_print_typ
> #ifdef CONFIG_PERF_EVENTS
> extern struct trace_event_call *
> create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> - bool is_return);
> + bool is_return, int max_active);
> extern void destroy_local_trace_kprobe(struct trace_event_call *event_call);
>
> extern struct trace_event_call *
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