Re: [RFC PATCH 3/4] vfio-ccw: Add a trace for asynchronous requests

[Eric Farman <farman@linux.ibm.com>]

On 10/15/19 5:54 AM, Steffen Maier wrote:
> On 10/14/19 8:08 PM, Eric Farman wrote:
>> Since the asynchronous requests are typically associated with
>> error recovery, let's add a simple trace when one of those is
>> issued to a device.
>>
>> Signed-off-by: Eric Farman <farman@linux.ibm.com>
>> ---
>>   drivers/s390/cio/vfio_ccw_fsm.c   |  4 ++++
>>   drivers/s390/cio/vfio_ccw_trace.c |  1 +
>>   drivers/s390/cio/vfio_ccw_trace.h | 26 ++++++++++++++++++++++++++
>>   3 files changed, 31 insertions(+)
>>
>> diff --git a/drivers/s390/cio/vfio_ccw_fsm.c
>> b/drivers/s390/cio/vfio_ccw_fsm.c
>> index d4119e4c4a8c..23648a9aa721 100644
>> --- a/drivers/s390/cio/vfio_ccw_fsm.c
>> +++ b/drivers/s390/cio/vfio_ccw_fsm.c
>> @@ -341,6 +341,10 @@ static void fsm_async_request(struct
>> vfio_ccw_private *private,
>>           /* should not happen? */
>>           cmd_region->ret_code = -EINVAL;
>>       }
>> +
>> +    trace_vfio_ccw_fsm_async_request(get_schid(private),
>> +                     cmd_region->command,
>> +                     cmd_region->ret_code);
>>   }
>>
>>   /*
>> diff --git a/drivers/s390/cio/vfio_ccw_trace.c
>> b/drivers/s390/cio/vfio_ccw_trace.c
>> index b37bc68e7f18..37ecbf8be805 100644
>> --- a/drivers/s390/cio/vfio_ccw_trace.c
>> +++ b/drivers/s390/cio/vfio_ccw_trace.c
>> @@ -9,5 +9,6 @@
>>   #define CREATE_TRACE_POINTS
>>   #include "vfio_ccw_trace.h"
>>
>> +EXPORT_TRACEPOINT_SYMBOL(vfio_ccw_fsm_async_request);
>>   EXPORT_TRACEPOINT_SYMBOL(vfio_ccw_fsm_event);
>>   EXPORT_TRACEPOINT_SYMBOL(vfio_ccw_io_fctl);
>> diff --git a/drivers/s390/cio/vfio_ccw_trace.h
>> b/drivers/s390/cio/vfio_ccw_trace.h
>> index 24a8152acfdf..4be2e36242e6 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_async_request,
>> +    TP_PROTO(struct subchannel_id schid,
>> +         int command,
>> +         int errno),
>> +    TP_ARGS(schid, command, errno),
>> +
>> +    TP_STRUCT__entry(
>> +        __field_struct(struct subchannel_id, schid)
> 
> Not sure: Does this allow the user to filter for fields of struct
> subchannel_id or can the user express a filter on the entire combined
> struct subchannel_id?

Good question...  I tried playing around with this a little bit, and
while format says it's using "REC->schid.foo", trying any combination to
get an element within schid just fails, citing some form of invalid
argument (the exact reason depends on what I try).  Harrumph.

> In the preceding patch you have the 3 parts of schid as explicit
> separate trace fields in the tracepoint.

Yeah, I did.  Why didn't I do that here?  :)

Well it seems that the one trace that exists (vfio_ccw_fsm_io_request
(nee vfio_ccw_fsm_io_fctl)), uses this same field_struct, instead of the
three-piece schid.  So, I need to change this in both the I/O and
asynchronous traces.

Thanks for the suggestions!
 - Eric

> 
>> +        __field(int, command)
>> +        __field(int, errno)
>> +    ),
>> +
>> +    TP_fast_assign(
>> +        __entry->schid = schid;
>> +        __entry->command = command;
>> +        __entry->errno = errno;
>> +    ),
>> +
>> +    TP_printk("schid=%x.%x.%04x command=%d errno=%d",
>> +          __entry->schid.cssid,
>> +          __entry->schid.ssid,
>> +          __entry->schid.sch_no,
>> +          __entry->command,
>> +          __entry->errno)
>> +);
>> +
>>   TRACE_EVENT(vfio_ccw_fsm_event,
>>       TP_PROTO(struct subchannel_id schid, int state, int event),
>>       TP_ARGS(schid, state, event),
>>
> 
>