Re: Interrupt time inflation on Xen

[Christoph Badura <bad%bsd.de@localhost>]

On Fri, Apr 15, 2016 at 12:52:36AM -0400, Thor Lancelot Simon wrote:
> It definitely does for me (that same dd, but from /dev/rsd0d, goes to
> 60% "Interrupt" time on pkgbuild).  I can't help noticing everyone who
> doesn't see the problem is using wd, while I see it with ciss or arcmsr.

I didn't mean to sound as if what you're seeing isn't real.  Sorry if I
did.

> I have trouble seeing how the SCSI code itself could be to blame, but I
> wonder if these two drivers have something in common (how they use bus_dma
> perhaps)?

I was wondering about that.  Especially since the wds are on ahcisata and
using DMA too.

> Now that Manuel fixed profiling, I can confirm at least part of your
> suspicion:
> 
> index % time    self  children    called     name
>                                                  <spontaneous>
> [1]     85.7   38.10    0.00                 hypercall_page [1]
> ----------------------------------------------- 
> 
> This is of course not a terribly useful profiling record since it cannot
> find any other functions in the call graph, so we cannot see which hypercall
> might be to blame.  I *think* the use of static inlines in hypercall.h is
> causing that problem, though I don't understand why the "callers" of those
> inline functions are missing from the call graph.
> 
> Still puzzling about how to work through this further.

Remove the static inlines and see if that lets the callers show up?  But I
guess you thought of that yourself.

--chris