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From ae618b75f2b158b4563ab94371b01b2951b1bfec Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Fri, 22 Oct 2021 18:00:27 +0100
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Subject: [PATCH] vddk: Document troubleshooting performance problems
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Document how to use -D vddk.stats=1 to diagnose performance problems
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with VDDK.
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(cherry picked from commit e491978c193f49010cc28ad344d0fb3c1b5ede35)
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---
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plugins/vddk/nbdkit-vddk-plugin.pod | 57 +++++++++++++++++++++++++++++
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1 file changed, 57 insertions(+)
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diff --git a/plugins/vddk/nbdkit-vddk-plugin.pod b/plugins/vddk/nbdkit-vddk-plugin.pod
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index e53d3286..5a426135 100644
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--- a/plugins/vddk/nbdkit-vddk-plugin.pod
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+++ b/plugins/vddk/nbdkit-vddk-plugin.pod
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@@ -475,6 +475,63 @@ and restarting the C<hostd> service:
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For more information see L<https://bugzilla.redhat.com/1614276>.
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+=head2 Troubleshooting performance problems
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+
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+VDDK has very uneven performance with some operations being very slow.
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+This plugin has options to allow you to debug performance issues. If
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+your application has a debug or diagnostic setting, add the following
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+nbdkit command line options:
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+
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+ -v -D nbdkit.backend.datapath=0 -D vddk.datapath=0 -D vddk.stats=1
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+
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+C<-v> enables verbose messages and the two datapath options I<disable>
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+the very verbose per-read/-write messages. C<-D vddk.stats=1> enables
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+a summary when nbdkit exits of the cumulative time taken in each VDDK
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+function, the number of times each function was called, and (for read
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+and write) the number of bytes transferred. An example of what those
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+stats look like can be found here:
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+L<https://gitlab.com/nbdkit/nbdkit/-/commit/5c80f0d290db45a679d55baf37ff39bacb8ce7ec>
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+
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+You can interpret the stats as follows:
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+
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+=over 4
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+
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+=item C<Read>
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+
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+The cumulative time spent waiting for VDDK to return from
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+C<VixDiskLib_Read> calls, the number of times this function was
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+called, and the total bytes read. You can use this to determine the
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+read bandwidth to the VMware server.
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+
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+=item C<Write>
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+
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+=item C<Flush>
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+
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+Same as above, but for writing and flushing writes.
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+
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+=item C<QueryAllocatedBlocks>
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+
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+This call is used to query information about the sparseness of the
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+remote disk. It is only available in VDDK E<ge> 6.7. The call is
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+notably very slow in all versions of VMware we have tested.
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+
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+=item C<Open>
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+
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+=item C<Close>
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+
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+=item C<ConnectEx>
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+
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+=item C<Disconnect>
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+
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+=item C<InitEx>
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+
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+=item C<Exit>
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+
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+The cumulative time spent connecting and disconnecting from the VMware
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+server, which can also be very slow.
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+
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+=back
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+
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=head1 SUPPORTED VERSIONS OF VDDK
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This plugin requires VDDK E<ge> 5.5.5, which in turn means that it
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--
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2.31.1
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