[Libguestfs] More parallelism in VDDK driver (was: Re: CFME-5.11.7.3 Perf. Tests)

[Richard W.M. Jones]

On Wed, Aug 05, 2020 at 05:40:18PM +0300, Nir Soffer wrote:
> On Wed, Aug 5, 2020 at 3:47 PM Richard W.M. Jones <rjones at redhat.com> wrote:
> >
> >
> > Here are some results anyway.  The command I'm using is:
> >
> > $ ./nbdkit -r -U - vddk \
> >     libdir=/path/to/vmware-vix-disklib-distrib \
> >     user=root password='***' \
> >     server='***' thumbprint=aa:bb:cc:... \
> >     vm=moref=3 \
> >     file='[datastore1] Fedora 28/Fedora 28.vmdk' \
> >     --run 'time /var/tmp/threaded-reads $unixsocket'
> >
> > Source for threaded-reads is attached.
> >
> > (1) Existing nbdkit VDDK plugin.
> >
> > NR_MULTI_CONN = 1
> > NR_CYCLES = 10000
> >
> > Note this is making 10,000 pread requests.
> >
> > real    1m26.103s
> > user    0m0.283s
> > sys     0m0.571s
> >
> > (2) VDDK plugin patched to support SERIALIZE_REQUESTS.
> >
> > NR_MULTI_CONN = 1
> > NR_CYCLES = 10000
> >
> > Note this is making 10,000 pread requests.
> >
> > real    1m26.755s
> > user    0m0.230s
> > sys     0m0.539s
> >
> > (3) VDDK plugin same as in (2).
> >
> > NR_MULTI_CONN = 8
> > NR_CYCLES = 10000
> >
> > Note this is making 80,000 pread requests in total.
> >
> > real    7m11.729s
> > user    0m2.891s
> > sys     0m6.037s
> >
> > My observations:
> >
> > Tests (1) and (2) are about the same within noise.
> >
> > Test (3) is making 8 times as many requests as test (1), so I think
> > it's fair to compare the 8 x time taken by test (1) (ie. the time it
> > would have taking to make 80,000 requests):
> >
> >   Test (1) * 8 = 11m28
> >   Test (3)     =  7m11
> 
> That's pretty good results, 62% faster.
> 
> What is the request size used? I would test 1, 2, 4, 8 MiB reads.

Randomly 512 bytes and 1M requests.  Yes we should probably test reads
of different sizes.

Rich.

> > So if we had a client which could actually use multi-conn then this
> > would be a reasonable win.  It seems like there's still a lot of
> > locking going on somewhere, perhaps inside VDDK or in the server.
> > It's certainly nowhere near a linear speedup.
> >
> > The patch does at least seem stable.  I'll post it in a minute.
> >
> > Rich.
> >
> > --
> > Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> > Read my programming and virtualization blog: http://rwmj.wordpress.com
> > libguestfs lets you edit virtual machines.  Supports shell scripting,
> > bindings from many languages.  http://libguestfs.org

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html