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Re: [Qemu-devel] [RFC] host and guest kernel trace merging
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [RFC] host and guest kernel trace merging |
Date: |
Fri, 4 Mar 2016 11:19:33 +0000 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Thu, Mar 03, 2016 at 02:35:01PM -0500, Luiz Capitulino wrote:
> trace-cmd-server
> ================
>
> Everything I described could look like this:
>
> # trace-cmd server [ in the host ]
> # trace-cmd record [ in the guest ]
> # trace-cmd report [ in the host, to merge the traces ]
>
> To achieve this, we need two things:
>
> 1. Add an interface to obtain the guest TSC offset from the
> host user-space.
>
> Maybe we could have a new sysfs directory, with a file
> per vCPU thread and the offset as contents? Or maybe
> just add a new entry to /proc/, like: /proc/TID/tsc-offset?
Yes, the interface is missing. In the past I have heard people using
trace events on the host to:
1. Collect tsc offsets
2. Track which vCPU is scheduled to a host CPU
So instead of relying on an interface they enable the relevant trace
events on the host and then parse the trace to collect this information.
However, it's a bad solution especially for tsc offsets since you may
wish to trace an already-running VM where the tracepoint that records
the tsc offset may not fire after startup (?).
Therefore, I agree that an interface for the tsc offset is needed.
> 2. Build a trace-cmd-server
>
> Which does the following:
>
> 1. Receive trace-cmd record commands from a guest,
> to be performed in the host
Sometimes the opposite is desirable: the host controls tracing inside
the guest. Any thoughts on this use case?
> 2. Read the TSC offset for vCPUs being traced
>
> 3. Read the CPU frequency for --ts2secs
>
> 4. Receive the guest.dat from the guest and store it together
> with the host's
>
> I'd suggest the default communication between guest and
> host be via networking. Then we add vsock support when it's
> available.
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- [Qemu-devel] [RFC] host and guest kernel trace merging, Luiz Capitulino, 2016/03/03
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Steven Rostedt, 2016/03/04
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Stefan Hajnoczi, 2016/03/07
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Steven Rostedt, 2016/03/07
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Eric Blake, 2016/03/07
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Steven Rostedt, 2016/03/07
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Paolo Bonzini, 2016/03/07
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Peter Xu, 2016/03/24
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Luiz Capitulino, 2016/03/24
- Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Peter Xu, 2016/03/24
Re: [Qemu-devel] [RFC] host and guest kernel trace merging, Peter Xu, 2016/03/24