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Date: Wed, 23 Nov 2022 11:18:06 +0800
From: Zheng Yejian <zhengyejian1@...wei.com>
To: <mhiramat@...nel.org>, <yujie.liu@...el.com>
CC: <bpf@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<rostedt@...dmis.org>, <zhengyejian1@...wei.com>
Subject: Re: [PATCH v2] tracing: Optimize event type allocation with IDA
On Fri, 11 Nov 2022 23:41:37 +0900,
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
> On Thu, 10 Nov 2022 10:03:19 +0800
> Zheng Yejian <zhengyejian1@...wei.com> wrote:
>
> > After commit 060fa5c83e67 ("tracing/events: reuse trace event ids after
> > overflow"), trace events with dynamic type are linked up in list
> > 'ftrace_event_list' through field 'trace_event.list'. Then when max
> > event type number used up, it's possible to reuse type number of some
> > freed one by traversing 'ftrace_event_list'.
> >
> > As instead, using IDA to manage available type numbers can make codes
> > simpler and then the field 'trace_event.list' can be dropped.
> >
> > Since 'struct trace_event' is used in static tracepoints, drop
> > 'trace_event.list' can make vmlinux smaller. Local test with about 2000
> > tracepoints, vmlinux reduced about 64KB:
> > before：-rwxrwxr-x 1 root root 76669448 Nov 8 17:14 vmlinux
> > after： -rwxrwxr-x 1 root root 76604176 Nov 8 17:15 vmlinux
> >
>
> This looks good to me.
>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Thanks for your kind ack, Masami!
But Yujie Liu <yujie.liu@...el.com> reported a problem that highly
reproducible after applying this patch:
Link: https://lore.kernel.org/lkml/54f23c9c-97ae-e326-5873-bfa5d2c81f52@intel.com/
So please DO NOT apply this patch before I find what happened about it.
--
Best regards,
Zheng Yejian
>
> Thanks
>
> > Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
> > ---
> > include/linux/trace_events.h | 1 -
> > kernel/trace/trace_output.c | 66 +++++++++---------------------------
> > 2 files changed, 16 insertions(+), 51 deletions(-)
> >
> > Changes since v1:
> > - Explicitly include linux/idr.h as suggested by Masami Hiramatsu
> > Link: https://lore.kernel.org/lkml/20221109222650.ce6c22e231345f6852f6956f@kernel.org/#t
> >
> > diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> > index 20749bd9db71..bb2053246d6a 100644
> > --- a/include/linux/trace_events.h
> > +++ b/include/linux/trace_events.h
> > @@ -136,7 +136,6 @@ struct trace_event_functions {
> >
> > struct trace_event {
> > struct hlist_node node;
> > - struct list_head list;
> > int type;
> > struct trace_event_functions *funcs;
> > };
> > diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> > index 67f47ea27921..f0ba97121345 100644
> > --- a/kernel/trace/trace_output.c
> > +++ b/kernel/trace/trace_output.c
> > @@ -11,6 +11,7 @@
> > #include <linux/kprobes.h>
> > #include <linux/sched/clock.h>
> > #include <linux/sched/mm.h>
> > +#include <linux/idr.h>
> >
> > #include "trace_output.h"
> >
> > @@ -21,8 +22,6 @@ DECLARE_RWSEM(trace_event_sem);
> >
> > static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly;
> >
> > -static int next_event_type = __TRACE_LAST_TYPE;
> > -
> > enum print_line_t trace_print_bputs_msg_only(struct trace_iterator *iter)
> > {
> > struct trace_seq *s = &iter->seq;
> > @@ -688,38 +687,23 @@ struct trace_event *ftrace_find_event(int type)
> > return NULL;
> > }
> >
> > -static LIST_HEAD(ftrace_event_list);
> > +static DEFINE_IDA(trace_event_ida);
> >
> > -static int trace_search_list(struct list_head **list)
> > +static void free_trace_event_type(int type)
> > {
> > - struct trace_event *e = NULL, *iter;
> > - int next = __TRACE_LAST_TYPE;
> > -
> > - if (list_empty(&ftrace_event_list)) {
> > - *list = &ftrace_event_list;
> > - return next;
> > - }
> > + if (type >= __TRACE_LAST_TYPE)
> > + ida_free(&trace_event_ida, type);
> > +}
> >
> > - /*
> > - * We used up all possible max events,
> > - * lets see if somebody freed one.
> > - */
> > - list_for_each_entry(iter, &ftrace_event_list, list) {
> > - if (iter->type != next) {
> > - e = iter;
> > - break;
> > - }
> > - next++;
> > - }
> > +static int alloc_trace_event_type(void)
> > +{
> > + int next;
> >
> > - /* Did we used up all 65 thousand events??? */
> > - if (next > TRACE_EVENT_TYPE_MAX)
> > + /* Skip static defined type numbers */
> > + next = ida_alloc_range(&trace_event_ida, __TRACE_LAST_TYPE,
> > + TRACE_EVENT_TYPE_MAX, GFP_KERNEL);
> > + if (next < 0)
> > return 0;
> > -
> > - if (e)
> > - *list = &e->list;
> > - else
> > - *list = &ftrace_event_list;
> > return next;
> > }
> >
> > @@ -761,28 +745,10 @@ int register_trace_event(struct trace_event *event)
> > if (WARN_ON(!event->funcs))
> > goto out;
> >
> > - INIT_LIST_HEAD(&event->list);
> > -
> > if (!event->type) {
> > - struct list_head *list = NULL;
> > -
> > - if (next_event_type > TRACE_EVENT_TYPE_MAX) {
> > -
> > - event->type = trace_search_list(&list);
> > - if (!event->type)
> > - goto out;
> > -
> > - } else {
> > -
> > - event->type = next_event_type++;
> > - list = &ftrace_event_list;
> > - }
> > -
> > - if (WARN_ON(ftrace_find_event(event->type)))
> > + event->type = alloc_trace_event_type();
> > + if (!event->type)
> > goto out;
> > -
> > - list_add_tail(&event->list, list);
> > -
> > } else if (WARN(event->type > __TRACE_LAST_TYPE,
> > "Need to add type to trace.h")) {
> > goto out;
> > @@ -819,7 +785,7 @@ EXPORT_SYMBOL_GPL(register_trace_event);
> > int __unregister_trace_event(struct trace_event *event)
> > {
> > hlist_del(&event->node);
> > - list_del(&event->list);
> > + free_trace_event_type(event->type);
> > return 0;
> > }
> >
> > --
> > 2.25.1
> >
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@...nel.org>
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