Messages in this thread | | | From | Ze Gao <> | Date | Thu, 3 Aug 2023 18:55:32 +0800 | Subject | Re: [RFC PATCH v6 4/5] sched, tracing: add to report task state in symbolic chars |
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On Thu, Aug 3, 2023 at 5:29 PM Steven Rostedt <rostedt@goodmis.org> wrote: > > On Thu, 3 Aug 2023 04:33:51 -0400 > Ze Gao <zegao2021@gmail.com> wrote: > > > Internal representations of task state are likely to be changed > > or ordered, and reporting them to userspace without exporting > > them as part of API is basically wrong, which can easily break > > a userspace observability tool as kernel evolves. For example, > > perf suffers from this and still reports wrong states as of this > > writing. > > > > OTOH, some masqueraded states like TASK_REPORT_IDLE and > > TASK_REPORT_MAX are also reported inadvertently, which confuses > > things even more and most userspace tools do not even take them > > into consideration. > > > > So add a new variable in company with the old raw value to > > report task state in symbolic chars, which are self-explaining > > and no further translation is needed. Of course this does not > > break any userspace tool. > > > > Note for PREEMPT_ACTIVE, we introduce 'p' to report it and use > > the old conventions for the rest. > > The above is actually good. > > > > > > Signed-off-by: Ze Gao <zegao@tencent.com> > > Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> > > Acked-by: Ian Rogers <irogers@google.com> > > --- > > include/trace/events/sched.h | 44 ++++++++++++++++++++++-------------- > > 1 file changed, 27 insertions(+), 17 deletions(-) > > > > diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h > > index 43492daefa6f..ae5b486cc969 100644 > > --- a/include/trace/events/sched.h > > +++ b/include/trace/events/sched.h > > @@ -6,6 +6,7 @@ > > #define _TRACE_SCHED_H > > > > #include <linux/kthread.h> > > +#include <linux/sched.h> > > #include <linux/sched/numa_balancing.h> > > #include <linux/tracepoint.h> > > #include <linux/binfmts.h> > > @@ -214,6 +215,27 @@ static inline short __trace_sched_switch_state(bool preempt, > > > > return state ? (1 << (state - 1)) : state; > > } > > + > > +static inline char __trace_sched_switch_state_char(bool preempt, > > + unsigned int prev_state, > > + struct task_struct *p) > > +{ > > + long state; > > + > > +#ifdef CONFIG_SCHED_DEBUG > > + WARN_ON_ONCE(p != current); > > +#endif /* CONFIG_SCHED_DEBUG */ > > + > > + /* > > + * For PREEMPT_ACTIVE, we introduce 'p' to report it and use the old > > + * conventions for the rest. > > + */ > > + if (preempt) > > + return 'p'; > > + > > + state = __task_state_index(prev_state, p->exit_state); > > + return task_index_to_char(state); > > +} > > #endif /* CREATE_TRACE_POINTS */ > > > > /* > > @@ -236,6 +258,7 @@ TRACE_EVENT(sched_switch, > > __array( char, prev_comm, TASK_COMM_LEN ) > > __array( char, next_comm, TASK_COMM_LEN ) > > __field( short, prev_state ) > > + __field( char, prev_state_char ) > > ), > > > > TP_fast_assign( > > @@ -246,26 +269,13 @@ TRACE_EVENT(sched_switch, > > memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN); > > memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN); > > __entry->prev_state = __trace_sched_switch_state(preempt, prev_state, prev); > > + __entry->prev_state_char = __trace_sched_switch_state_char(preempt, prev_state, prev); > > /* XXX SCHED_DEADLINE */ > > ), > > > > - TP_printk("prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==> next_comm=%s next_pid=%d next_prio=%d", > > - __entry->prev_comm, __entry->prev_pid, __entry->prev_prio, > > - > > - (__entry->prev_state & (TASK_REPORT_MAX - 1)) ? > > - __print_flags(__entry->prev_state & (TASK_REPORT_MAX - 1), "|", > > - { TASK_INTERRUPTIBLE, "S" }, > > - { TASK_UNINTERRUPTIBLE, "D" }, > > - { __TASK_STOPPED, "T" }, > > - { __TASK_TRACED, "t" }, > > - { EXIT_DEAD, "X" }, > > - { EXIT_ZOMBIE, "Z" }, > > - { TASK_PARKED, "P" }, > > - { TASK_DEAD, "I" }) : > > - "R", > > I just realized, I have user space code that looks at this. As in the format file we have: > > print fmt: "prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==> next_comm=%s next_pid=%d next_prio=%d", REC->prev_comm, REC->prev_pid, REC->prev_prio, (REC->prev_state & ((((0x00000000 | 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 | 0x00000010 | 0x00000020 | 0x00000040) + 1) << 1) - 1)) ? __print_flags(REC->prev_state & ((((0x00000000 | 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 | 0x00000010 | 0x00000020 | 0x00000040) + 1) << 1) - 1), "|", { 0x00000001, "S" }, { 0x00000002, "D" }, { 0x00000004, "T" }, { 0x00000008, "t" }, { 0x00000010, "X" }, { 0x00000020, "Z" }, { 0x00000040, "P" }, { 0x00000080, "I" }) : "R", REC->prev_state & (((0x00000000 | 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 | 0x00000010 | 0x00000020 | 0x00000040) + 1) << 1) ? "+" : "", REC->next_comm, REC->next_pid, REC->next_prio > > And I have used this in applications to find out what values "S" and "D" > are. > > So, we need to keep that still. But we can add the prev_state_char to the > output too. > > "prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s[%c] ==> next_comm=%s next_pid=%d next_prio=%d"
Good point!
But I see Peter has strong opinions over this change badly. So I'm not sure if it's worth the effort to push this anymore :/ And apparently We failed to convince each other over this problem.
How about we only keep all the fixing patches and throw away this 'prev_state_char' thing?
Again, I'm not meant to upset anyone here. But Tons of thanks for your sage reviews on this.
Thoughts?
Thanks, Ze
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