Re: [RFC PATCH 2/4] vfio-ccw: Trace the FSM jumptable

[Steffen Maier <maier@linux.ibm.com>]

On 10/15/19 3:53 PM, Cornelia Huck wrote:
> On Tue, 15 Oct 2019 12:01:12 +0200
> Steffen Maier <maier@linux.ibm.com> wrote:
> 
>> On 10/14/19 8:08 PM, Eric Farman wrote:
>>> It would be nice if we could track the sequence of events within
>>> vfio-ccw, based on the state of the device/FSM and our calling
>>> sequence within it.  So let's add a simple trace here so we can
>>> watch the states change as things go, and allow it to be folded
>>> into the rest of the other cio traces.
>>>
>>> Signed-off-by: Eric Farman <farman@linux.ibm.com>
>>> ---
>>>    drivers/s390/cio/vfio_ccw_private.h |  1 +
>>>    drivers/s390/cio/vfio_ccw_trace.c   |  1 +
>>>    drivers/s390/cio/vfio_ccw_trace.h   | 26 ++++++++++++++++++++++++++
>>>    3 files changed, 28 insertions(+)
> 
> (...)
> 
>>> diff --git a/drivers/s390/cio/vfio_ccw_trace.h b/drivers/s390/cio/vfio_ccw_trace.h
>>> index 2a2937a40124..24a8152acfdf 100644
>>> --- a/drivers/s390/cio/vfio_ccw_trace.h
>>> +++ b/drivers/s390/cio/vfio_ccw_trace.h
>>> @@ -17,6 +17,32 @@
>>>
>>>    #include <linux/tracepoint.h>
>>>
>>> +TRACE_EVENT(vfio_ccw_fsm_event,
>>> +	TP_PROTO(struct subchannel_id schid, int state, int event),
>>> +	TP_ARGS(schid, state, event),
>>> +
>>> +	TP_STRUCT__entry(
>>> +		__field(u8, cssid)
>>> +		__field(u8, ssid)
>>> +		__field(u16, schno)
>>> +		__field(int, state)
>>> +		__field(int, event)
>>> +	),
>>> +
>>> +	TP_fast_assign(
>>> +		__entry->cssid = schid.cssid;
>>> +		__entry->ssid = schid.ssid;
>>> +		__entry->schno = schid.sch_no;
>>> +		__entry->state = state;
>>> +		__entry->event = event;
>>> +	),
>>> +
>>> +	TP_printk("schid=%x.%x.%04x state=%x event=%x",
>>
>> /sys/kernel/debug/tracing/events](0)# grep -R '%[^%]*x'
>>
>> Many existing TPs often seem to format hex output with a 0x prefix (either
>> explicit with 0x%x or implicit with %#x). Since some of your other TPs also
>> output decimal integer values, I wonder if a distinction would help
>> unexperienced TP readers.
> 
> I generally agree. However, we explicitly don't want to do that for
> schid formatting (as it should match the bus id). For event, it might
> become relevant should we want to introduce a high number of new events
> in the future (currently, there's a grand total of four events.)

Yeah, thanks for clarifying. I meant just state and event, not schid.

> 
>>
>>> +		__entry->cssid, __entry->ssid, __entry->schno,
>>> +		__entry->state,
>>> +		__entry->event)
>>> +);
>>> +
>>>    TRACE_EVENT(vfio_ccw_io_fctl,
>>>    	TP_PROTO(int fctl, struct subchannel_id schid, int errno, char *errstr),
>>>    	TP_ARGS(fctl, schid, errno, errstr),
>>>    
>>
>>
> 


-- 
Mit freundlichen Gruessen / Kind regards
Steffen Maier

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