On 08/03/2010 05:53 PM, Richard W.M. Jones wrote:
Total saving: 115ms.
815 ms by my arithmetic.
no, not true, 115ms.
If you bypass creating the initrd/cdrom (700 ms) and loading it (115ms)
you save 815ms.
You also save 3*N-2*P memory where N is the size of your initrd and
P is the actual amount used by the guest.
Can you explain this?
(assuming ahead-of-time image generation)
initrd:
qemu reads image (host pagecache): N
qemu stores image in RAM: N
guest copies image to its RAM: N
guest faults working set (no XIP): P
total: 3N+P
initramfs:
qemu reads image (host pagecache): N
qemu stores image: N
guest copies image: N
guest extracts image (XIP): N
total: 4N
cdrom:
guest faults working set: P
kernel faults working set: P
total: 2P
difference: 3N-P or 4N-2P depending on model
Loading a file into memory is plenty fast if you use the standard
interfaces. -kernel -initrd is a specialized interface.
Why bother with any command line options at all? After all, they keep
changing and causing problems for qemu's users ... Apparently we're
all doing stuff "wrong", in ways that are never explained by the
developers.
That's a real problem. It's hard to explain the intent behind
something, especially when it's obvious to the author and not so obvious
to the user. However making everything do everything under all
circumstances has its costs.
-kernel and -initrd is a developer's interface intended to make life
easier for users that use qemu to develop kernels. It was not intended
as a high performance DMA engine. Neither was the firmware
_configuration_ interface. That is what virtio and to a lesser extent
IDE was written to perform. You'll get much better results from them.
--
error compiling committee.c: too many arguments to function
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