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Re: [Xen-devel] unconditionally enable the trace buffer

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

* 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'
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

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