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

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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.

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