[Qemu-devel] Re: [RFC PATCH 05/20] Introduce put_vector() and get_vector to QEMUFile and qemu_fopen_ops().

[Avi Kivity]

On 04/23/2010 04:22 PM, Anthony Liguori wrote:
> > I currently don't have data, but I'll prepare it.
> > There were two things I wanted to avoid.
> >
> > 1. Pages to be copied to QEMUFile buf through qemu_put_buffer.
> > 2. Calling write() everytime even when we want to send multiple pages 
> > at once.
> >
> > I think 2 may be neglectable.
> > But 1 seems to be problematic if we want make to the latency as small 
> > as possible, no?
>
>
> Copying often has strange CPU characteristics depending on whether the 
> data is already in cache.  It's better to drive these sort of 
> optimizations through performance measurement because changes are not 
> always obvious.

Copying always introduces more cache pollution, so even if the data is 
in the cache, it is worthwhile (not disagreeing with the need to measure).

--
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.