On 03/11/2010 09:46 AM, Sheng Yang wrote:
On Thursday 11 March 2010 15:36:01 Avi Kivity wrote:
On 03/11/2010 09:20 AM, Sheng Yang wrote:
Currently we can only get the cpu_stat of whole guest as one. This patch
enhanced cpu_stat with more detail, has guest_system and guest_user cpu
time statistics with a little overhead.
Signed-off-by: Sheng Yang<sheng@xxxxxxxxxxxxxxx>
---
This draft patch based on KVM upstream to show the idea. I would split it
into more kernel friendly version later.
The overhead is, the cost of get_cpl() after each exit from guest.
This can be very expensive in the nested virtualization case, so I
wouldn't like this to be in normal paths. I think detailed profiling
like that can be left to 'perf kvm', which only has overhead if enabled
at runtime.
Yes, that's my concern too(though nested vmcs/vmcb read already too expensive,
they should be optimized...).
Any ideas on how to do that? Perhaps use paravirt_ops to covert the
vmread into a memory read? We store the vmwrites in the vmcs anyway.
The other concern is, perf alike mechanism would
bring a lot more overhead compared to this.
Ordinarily users won't care if time is spent in guest kernel mode or
guest user mode. They want to see which guest is imposing a load on a
system. I consider a user profiling a guest from the host an advanced
and rarer use case, so it's okay to require tools and additional
overhead for this.
For example you can put the code to note the cpl in a tracepoint which
is enabled dynamically.
Yanmin have already implement "perf kvm" to support this. We are just arguing
if a normal top-alike mechanism is necessary.
I am also considering to make it a feature that can be disabled. But seems it
make things complicate and result in uncertain cpustat output.
I'm not even sure that guest time was a good idea.
--
error compiling committee.c: too many arguments to function
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
