Re: [Qemu-devel] [PATCH 07/15] qapi: use mmap for QmpInputVisitor

["Daniel P. Berrange" <berrange@redhat.com>]

On Tue, Jun 28, 2016 at 11:17:59AM +0100, Dr. David Alan Gilbert wrote:
> * Daniel P. Berrange (berrange@redhat.com) wrote:
> > On Tue, Jun 28, 2016 at 11:39:03AM +0200, Peter Lieven wrote:
> > > Am 28.06.2016 um 11:29 schrieb Dr. David Alan Gilbert:
> > > > * Peter Lieven (pl@kamp.de) wrote:
> > > > > this struct is approx 75kB
> > > > I wonder why it's so large.
> > > > 
> > > > The stack size in QmpInputVisitor; it's got a 1024 element stack
> > > > (QIV_STACK_SIZE) and I bet we never use anywhere near that.
> > > > 
> > > > But even then that's 1024 * a 3 pointer stack object, 24 bytes -
> > > > I don't see where the rest of that 75kB comes from.
> > > 
> > > Sorry, I had a wrong size in mind. Its 24736 bytes. But thats
> > > still larger than expecetd, right?
> > > 
> > > > I'm a little wary about turning all these malloc's into mmap's
> > > > because we do seem to use things like input visitors for small
> > > > things; don't the cost of doing the mmap's add up in time
> > > > instead of space?
> > > 
> > > Sure, we should discuss this. The series should act as a base for
> > > discussion.
> > > 
> > > None of the things I changed into mmap are continously called
> > > during VM runtime. So it most likely only happens at setup of the
> > > vServer.
> > 
> > QmpInputVisitor is used to parse all QMP monitor commands, so will
> > be used continuously throughout life of QEMU, often very frequently.
> > eg When migration is running many monitor commands per second are
> > expected
> 
> Does the same input visitor get reused by each command?

Opps, actually no i'm wrong, its only used by the 'object_add' command
but that does allocate a new one for each invokation.


Regards,
Daniel
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