Messages in this thread | | | Date | Thu, 21 Nov 2019 08:13:27 +0100 | From | Oleksandr Natalenko <> | Subject | Injecting delays into block layer |
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Hi Paolo et al.
I have a strong suspect that something is going wrong when the underlying block device responds with a large delay. What makes me thinking so is that I use a VM on some cloud provider, and they have substantial block device latency resulting in permanently high (~20%) iowait. It spikes occasionally when their cluster is overloaded, and when that happens, the I/O in my VM may stop and never recover. This is a rare occasion, but it really happens.
What's worse, so far I've seen such a behaviour with BFQ only. I'm still testing other schedulers though.
Important note: I have no strict evidences that this is *the* case, thus I'm asking for some suggestions. My idea is to fire up a local VM and inject delays to a block device while performing some I/O from within the VM.
So the question is: how can those delays be injected? Using dm-delay? Can those delays be random?
Thanks in advance.
-- Oleksandr Natalenko (post-factum)
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