Messages in this thread | | | Date | Thu, 3 Aug 2023 05:18:26 -0400 | From | Steven Rostedt <> | Subject | Re: [RFC PATCH v6 3/5] sched, tracing: reorganize fields of switch event struct |
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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.
See the difference?
> > #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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