Re: Hi,something about the xentrace tool

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

rickey berkeley wrote:
> Based on trace source code(xen/common/trace.c),dom0 tracing the event 
> which are enabled.
>
> xen initialize tracing buffer for each cpu,trace buffer size (in 
> pages) in kenel space is defined by opt_tbuf_size.
> The tracing buf use loop structure.
>
> I guess when the tracing data increase rapidly ,and xentrace tool in 
> user space does not take them immediately.
> Some tracing data will lost.Maybe relayfs or something else can solve 
> this problem.
>

I added a basic flow control mechanism to the trace buffer system a few 
months ago. You can see an example of how to use it in tools/xenmon. The 
way it works is that as trace records are generated, a software 
interrupt is generated when the trace buffer gets filled to a certain 
point. The user space tools can use select() on an event channel to find 
out about these interrupts. See tools/xenmon/xenbaked.c for exact 
programming details. This code has not been copied into xentrace yet; 
Feel free to do so yourself if you think it's necessary.

Rob