[Qemu-devel] block migration and MAX_IN_FLIGHT_IO

[Peter Lieven]

Hi,


I stumbled across the MAX_INFLIGHT_IO field that was introduced in 2015 and was 
curious what was the reason

to choose 512MB as readahead? The question is that I found that the source VM 
gets very unresponsive I/O wise

while the initial 512MB are read and furthermore seems to stay unreasponsive if 
we choose a high migration speed

and have a fast storage on the destination VM.


In our environment I modified this value to 16MB which seems to work much 
smoother. I wonder if we should make

this a user configurable value or define a different rate limit for the block 
transfer in bulk stage at least?


Peter