Re: [Xen-devel] x86-64 Net Performance

[Alexander Charbonnet <alexander@xxxxxxxxxxxxxx>]

I did `apt-get source glibc`, edited debian/sysdeps/amd64.mk to comment out 
the couple of lines enabling NPTL, then used dpkg-buildpackage to generate 
new .debs.

Your skepticism was warranted; I double-checked my changes to that file, and I 
had also disabled a line that set -O3 for the compile.  This seems to account 
for the performance difference on native; recompiling with -O3 intact slows 
things down to normal.  So the conclusion is that NPTL / TLS doesn't make 
much difference.

However, it's kind of odd that disabling -O3 would make things faster on 
native, but have no effect on Xen.

Alex


On Sunday 09 October 2005 04:18 am, Ian Pratt wrote:
> > Update: I went ahead and compiled glibc without TLS / NPTL.
>
> For 64 bit Xen you don't need to worry about TLS/NPTL.
>
> > Also, I realized that I wasn't allocating all my physical
> > memory to Domain0 for these tests, so I was giving Xen a
> > disadvantage.  It didn't change much, but those tests have
> > been re-done.
> >
> > Here's the odd thing: disabling TLS for 64-bit improved
> > native performance by around 10%, but had no effect on Xen.
>
> How did you disable TLS on 64 bit? It's odd that it would have any
> effect on native or xen, let alone such a dramatic one. Are you sure
> about this test?
>
> >                 Native  Domain0 Penalty
> > 64-bit TLS      50.2    65.0    29.5%
> > 64-bit no TLS   44.8    65.0    45.1%
> > 32-bit TLS      59.6    59.5    -0.2%
> > 32-bit no TLS   59.6    60.2     1.0%
>
> It looks like we need to investigate x86_64 networking performance. We
> may well not be getting the pipelining that we do in 32bit, though I
> can't immediately think why,
>
> Ian

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