RwLock::read for UFT hits, kstats use AtomicU64
#636
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This PR replaces the per-`Port` `KMutex` with a `KRwLock`. This allows ioctls to read port state without preventing packets from being served. This also prevents successful UFT hits from blocking one another on the port for any length of time. A requirement is that we move to atomic accesses on kstat values, which allows us to update kstats from outside a write-lock on the port. The odd thing is that there doesn't seem to be a performance improvement (in Mbps). Contention according to lockstat is solved, and apparently the time spent in `xde_rx`/`xde_mc_tx` is reduced -- we're no longer: * S2C -- the 3rd and 10th most spin-happy locks, * C2S -- the 2rd and 3rd most spin-happy locks. Nor are we egregiously blocking on the port lock.
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This PR replaces the per-
PortKMutexwith aKRwLock. This allowsioctls to read port state without preventing packets from being served.
This also prevents successful UFT hits from blocking one another on the
port for any length of time.
A requirement is that we move to atomic accesses on kstat values, which
allows us to update kstats from outside a write-lock on the port.
The odd thing is that there doesn't seem to be a performance
improvement (in Mbps). Contention according to lockstat is solved, and
apparently the time spent in
xde_rx/xde_mc_txis reduced -- we're nolonger:
Nor are we egregiously blocking on the port lock.