Messages in this thread | | | From | Ze Gao <> | Date | Thu, 3 Aug 2023 20:57:35 +0800 | Subject | Re: [RFC PATCH v6 3/5] sched, tracing: reorganize fields of switch event struct |
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On Thu, Aug 3, 2023 at 5:18 PM Steven Rostedt <rostedt@goodmis.org> wrote: > > On Thu, 3 Aug 2023 04:33:50 -0400 > Ze Gao <zegao2021@gmail.com> wrote: > > > Report prioritiy and prev_state in 'short' to save some buffer > > space. And also reorder the fields so that we take struct > > alignment into consideration to make the record compact. > > If I were to write this, I would have wrote: > > The prev_state field in the sched_switch event is assigned by > __trace_sched_switch_state(). The largest number that function will return > is TASK_REPORT_MAX which is just 0x100. There's no reason that the > prev_state field is a full 32 bits when it is using just 9 bits max. In > order to save space on the ring buffer, shrink the prev_state to 16 bits > (short). > > Also, change the positions of the other fields to accommodate the short > value of prev_state to eliminate any holes that were created in the > structure.
Thanks for this elaboration! But I see Peter have comments on this, I'll wait to see these resolved and then send my new changelog.
Thanks, Ze
> > > > #ifdef CREATE_TRACE_POINTS > > -static inline long __trace_sched_switch_state(bool preempt, > > +static inline short __trace_sched_switch_state(bool preempt, > > unsigned int prev_state, > > struct task_struct *p) > > { > > unsigned int state; > > > > #ifdef CONFIG_SCHED_DEBUG > > - BUG_ON(p != current); > > + WARN_ON_ONCE(p != current); > > #endif /* CONFIG_SCHED_DEBUG */ > > The above needs to be a separate patch. > > -- Steve > > > > > /* > > @@ -229,23 +229,23 @@ TRACE_EVENT(sched_switch, > > TP_ARGS(preempt, prev, next, prev_state), > > > > TP_STRUCT__entry( > > - __array( char, prev_comm, TASK_COMM_LEN ) > > __field( pid_t, prev_pid ) > > - __field( int, prev_prio ) > > - __field( long, prev_state ) > > - __array( char, next_comm, TASK_COMM_LEN ) > > __field( pid_t, next_pid ) > > - __field( int, next_prio ) > > + __field( short, prev_prio ) > > + __field( short, next_prio ) > > + __array( char, prev_comm, TASK_COMM_LEN ) > > + __array( char, next_comm, TASK_COMM_LEN ) > > + __field( short, prev_state ) > > ), > > > > TP_fast_assign( > > - memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN); > > - __entry->prev_pid = prev->pid; > > - __entry->prev_prio = prev->prio; > > - __entry->prev_state = __trace_sched_switch_state(preempt, prev_state, prev); > > + __entry->prev_pid = prev->pid; > > + __entry->next_pid = next->pid; > > + __entry->prev_prio = (short) prev->prio; > > + __entry->next_prio = (short) next->prio; > > memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN); > > - __entry->next_pid = next->pid; > > - __entry->next_prio = next->prio; > > + memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN); > > + __entry->prev_state = __trace_sched_switch_state(preempt, prev_state, prev); > > /* XXX SCHED_DEADLINE */ > > ), > > >
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