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

[Nir Soffer]

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.

> 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,
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