Re: [PATCH RFC 0/4]Porting Xentrace to kvm

[Jan Kiszka <jan.kiszka@web.de>]

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Avi Kivity wrote:
> Liu, Eric E wrote:
>> Hi,
>> The following patches port xentrace to kvm which is useful for
>> performance tuning and debugging.
>>
>> It is designed to allow debugging traces of kvm to be generated on
>> Up/Smp machines. Each trace entry is outputted in a trace ring buffer
>> for per cpu which is mapped to userspace, and the userspace tools can
>> analyze the data according to some formats definitions.
>>
>> Since we already have had debugfs_entries and some other kernel debug
>> mechanism to use, does this kvmtrace make sense? Any comment is
>> welcomed. 
>>   
> 
> This looks very useful.  While kvm_stat provides good data, this is much 
> more in depth.
> 
> The kernel already contains a method of transferring percpu data to 
> userspace; see Documentation/filesystems/relay.txt.  It supports mmap() 
> and read().  Please see if it is a good fit.

I would also suggest to use the new kernel standard for instrumentation:
trace_mark().

This would also allow to reuse the trace points with other tracer and
maybe even obsolete a separate transportation channel, e.g. when LTTng
is once :-/ merged.

Jan


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