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Message-ID: <20230725083357.GA3765278@hirez.programming.kicks-ass.net>
Date: Tue, 25 Jul 2023 10:33:57 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Ze Gao <zegao2021@...il.com>
Cc: Ingo Molnar <mingo@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Jiri Olsa <jolsa@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, Ze Gao <zegao@...cent.com>
Subject: Re: [RFC PATCH 1/3] sched, tracing: report task state in symbolic
chars instead
On Tue, Jul 25, 2023 at 03:22:52PM +0800, Ze Gao wrote:
> @@ -197,13 +198,6 @@ static inline long __trace_sched_switch_state(bool preempt,
> BUG_ON(p != current);
> #endif /* CONFIG_SCHED_DEBUG */
>
> - /*
> - * Preemption ignores task state, therefore preempted tasks are always
> - * RUNNING (we will not have dequeued if state != RUNNING).
> - */
> - if (preempt)
> - return TASK_REPORT_MAX;
> -
> /*
> * task_state_index() uses fls() and returns a value from 0-8 range.
> * Decrement it by 1 (except TASK_RUNNING state i.e 0) before using
> @@ -212,7 +206,16 @@ static inline long __trace_sched_switch_state(bool preempt,
> */
> state = __task_state_index(prev_state, p->exit_state);
>
> - return state ? (1 << (state - 1)) : state;
> + /*
> + * Preemption ignores task state, therefore preempted tasks are always
> + * RUNNING (we will not have dequeued if state != RUNNING).
> + * Here, we use 'p' to denote this case and only for this case.
> + */
> + if (preempt)
> + return 'p';
> +
I don't get this move, why compute state before this return?
> +
> + return task_index_to_char(state);
> }
> #endif /* CREATE_TRACE_POINTS */
>
> @@ -232,7 +235,7 @@ TRACE_EVENT(sched_switch,
> __array( char, prev_comm, TASK_COMM_LEN )
> __field( pid_t, prev_pid )
> __field( int, prev_prio )
> - __field( long, prev_state )
> + __field( char, prev_state )
> __array( char, next_comm, TASK_COMM_LEN )
> __field( pid_t, next_pid )
> __field( int, next_prio )
This is a format change and will likely break a ton of programs :/
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