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-ppc" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
