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SubjectRe: [RFC PATCH 2/2] trace: allocate temparary buffer for trace output usage
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thanks for remind, will check and use it.


thanks

On 12/14/2022 10:25 PM, Steven Rostedt wrote:
> On Wed, 14 Dec 2022 22:11:42 +0800
> Linyu Yuan <quic_linyyuan@quicinc.com> wrote:
>
>> there is one dwc3 trace event declare as below,
>> DECLARE_EVENT_CLASS(dwc3_log_event,
>> TP_PROTO(u32 event, struct dwc3 *dwc),
>> TP_ARGS(event, dwc),
>> TP_STRUCT__entry(
>> __field(u32, event)
>> __field(u32, ep0state)
>> __dynamic_array(char, str, DWC3_MSG_MAX)
>> ),
>> TP_fast_assign(
>> __entry->event = event;
>> __entry->ep0state = dwc->ep0state;
>> ),
>> TP_printk("event (%08x): %s", __entry->event,
>> dwc3_decode_event(__get_str(str), DWC3_MSG_MAX,
>> __entry->event, __entry->ep0state))
>> );
>> the problem is when trace function called, it will allocate up to
>> DWC3_MSG_MAX bytes from trace event buffer, but never fill the buffer
>> during fast assignment, it only fill the buffer when output function are
>> called, so this means if output function are not called, the buffer will
>> never used.
>>
>> add __alloc_buf() and __get_buf() which will not allocate event buffer
>> when trace function called, but when trace output function called, it will
>> kmalloc buffer with size DWC3_MSG_MAX for temprary usage and free it
>> before trace output function return.
> This looks exactly like what the trace_seq *p is to be used for.
>
> static notrace enum print_line_t \
> trace_raw_output_##call(struct trace_iterator *iter, int flags, \
> struct trace_event *trace_event) \
> { \
> struct trace_seq *s = &iter->seq; \
> struct trace_seq __maybe_unused *p = &iter->tmp_seq; \
> ^^^^^^^^^^^^^^^^^^^^
>
> struct trace_event_raw_##call *field; \
> int ret; \
> \
> field = (typeof(field))iter->ent; \
> \
> ret = trace_raw_output_prep(iter, trace_event); \
> if (ret != TRACE_TYPE_HANDLED) \
> return ret; \
> \
> trace_event_printf(iter, print); \
> \
> return trace_handle_return(s); \
> } \
>
> That is a trace_seq buffer that is for temporary usage during the output.
>
> See:
> include/trace/events/libata.h
> include/trace/events/scsi.h
>
> As well as the macros trace_print_bitmask_seq(), trace_print_flags_seq(),
> trace_print_symbols_seq(), etc.
>
> -- Steve
>

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