* Alexander Graf <[email protected]> wrote:
> So the simple rule is: don't register a coalesced MMIO region for a
> region where latency matters. [...]
So my first suspicion is confirmed.
A quick look at Qemu sources shows that lots of drivers are using
coalesced_mmio without being aware of the latency effects and only
one seems to make use of qemu_flush_coalesced_mmio_buffer(). Drivers
like hw/e1000.c sure look latency critical to me.
So i maintain my initial opinion: this is a pretty dangerous
'optimization' that should be used with extreme care: i can tell it
you with pretty good authority that latency problems are much more
easy to introduce than to find and remove ...
Thanks,
Ingo
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