Re: unconditionally enable the trace buffer

[Rob Gardner <rob.gardner@hp.com>]

Ian Pratt wrote:

>I haven't looked at xentrace in a while, but last time I did it could
>seriously do with some tidying up. Here's a list of features I'd like to
>see it have. I'd be grateful if you could tell me what the current state
>is:
>
>* ability to turn on/off via hypercall
>  
>

Not currently implemented, but would not be difficult to add.

>* trace events grouped by type, with a bitmap to enable the event types
>of interest
>  
>

This functionality is in there already.

>* ability to set the per CPU tracebuffer size when turning it on
>  
>

Partially; You can enable the trace buffer on the xen (boot) command 
line, and you can specify the trace buffer size there. You cannot change 
the size dynamically.

>* ability for the user-space reader to explicitly block (select on fd)
>on an eventchn notification that the buffer is e.g. half full. (reader
>should write out all the pages that are full of trace events)
>  
>
Not done.

>* user space reader should log when it misses blocks of events
>(overwrite last trace message in buffer with a special 'missed X events'
>message) 
>
>  
>
Not done, but my XenMon patch includes a change to the trace buffer code 
to help with this. I've added a "sequence number" to each trace record 
which can be used to detect when blocks of events have been missed.

Rob Gardner