[prev in list] [next in list] [prev in thread] [next in thread] 

List:       kvm
Subject:    Re: [PATCH 0 of 6] PowerPC KVM patches for 2.6.29
From:       Hollis Blanchard <hollisb () us ! ibm ! com>
Date:       2008-12-03 19:22:13
Message-ID: 1228332133.10084.42.camel () localhost ! localdomain
[Download RAW message or body]

On Wed, 2008-12-03 at 19:06 +0200, Avi Kivity wrote:
> Hollis Blanchard wrote:
> >
> >> I'm not thrilled about the private exit timing statistics gathering, 
> >> hopefully it can be morphed into the more general framework.
> >>     
> >
> > Is there anything in particular you have in mind? I think it could be
> > generally useful, but since x86 has hardware support for performance
> > monitoring, oprofile will already give you more accurate information. Of
> > course, I don't think you could extract standard deviation from an
> > oprofile report, and that has been very useful for us because it can
> > tell us e.g. 99% of instruction emulation is handled in the minimum
> > amount of time, but 1% takes hundreds of ms.
> >   
> 
> kvmtrace is basically a bunch of trace_marker()s sprinkled around the 
> code.  the marker infrastructure allow you to attach a callback to the 
> markers, where you can do the accounting.  The nice thing it can be 
> switched off at runtime, being replaced by a nop so 
> compiled-in-but-disabled overhead is very low.

However, we grab timestamps extremely early and late in the exit
handlers, in contexts from which it is not safe to call C code. This is
really important because we need to be able to measure the time spent in
the interrupt handler assembly. For x86 that may be confined to a simple
inline asm statement, but the code in
arch/powerpc/kvm/booke_interrupts.S is non-trivial and worth measuring.

-- 
Hollis Blanchard
IBM Linux Technology Center

--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
[prev in list] [next in list] [prev in thread] [next in thread]