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Re: [Qemu-devel] [PATCH v4 0/6] hypertrace: Lightweight guest-to-QEMU tr

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [PATCH v4 0/6] hypertrace: Lightweight guest-to-QEMU trace channel
Date: Mon, 9 Jan 2017 16:28:47 +0000
User-agent: Mutt/1.7.1 (2016-10-04)

On Mon, Dec 26, 2016 at 09:34:38PM +0100, LluĂ­s Vilanova wrote:
> The hypertrace channel allows guest code to emit events in QEMU (the host) 
> using
> its tracing infrastructure (see "docs/trace.txt"). This works in both 'system'
> and 'user' modes, is architecture-agnostic and introduces minimal noise on the
> guest.
> See first commit for a full description, use-cases and an example.

As mentioned previously, the -system mode "1 vmexit per trace event"
approach is too heavyweight for for performance analysis or high
frequency tracing.  It might be useful for things like system bringup or
TCG development though.

The -user approach is more promising because overheads are lower when
guest code really just jumps into QEMU code.

I have left comments on the patches.

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