Re: [PATCH 3/3] apple-nvme: defer cache flushes by a specified amount

quoted

Cache flushes on the M1 nvme are really slow, taking 17-18 msec to
complete. This can slow down workloads considerably, pure random writes
end up being bound by the flush latency and hence run at 55-60 IOPS.

Add a deferred flush work around to provide better performance, at a
minimal risk. By default, flushes are delayed at most 1 second, but this
is configurable.

With this work-around, a pure random write workload runs at ~12K IOPS
rather than 56 IOPS.

Just as last time this really is not a driver feature.  Cache flushes
are slow on consumer hardware, it's just apple is worse than usual.
Breaking file system transactional guarantee by ignoring data integrity
command in the driver is a no-go.

If we want to allow an opt-in policy for those whole feel adventurous,
it belongs into the core flush state machine.  Fortunately the patch
author seems qualified to touch that :)

Fair enough. I didn't realize this patch was previously discussed, my
apologies. I'll drop this change in v2, and hopefully somebody is
inspired later to do that 'adventure'.