On 06/11/2014 02:26 PM, Salz, Rich wrote:
What kinds of operations are protected by read locks?
Looking at almost any of the global data structures, such as error tables, OID
tables, and so on.
Often, RW locks aren't a win because maintaining just the read locks (without
any writers) introduces contention at the hardware level, and parallelism does
not increase all that much as a result. Paul McKenney's dissertation on RCU
has some examples.
We've monitored one of our applications, an SSL-terminating HTTP proxy server, under
load. Of all the mutexes (futex, actually) in the system, the "error" lock is
the most highly contended one. I'll see about posting some statistics.
Is this CRYPTO_LOCK_ERR? It would be interesting which locking path
actually triggers the contention. If it's the thread-local storage
re-implementation, it should be possible to use an ERR implementation
which uses native thread-local storage, which should be mostly
contention-free.
--
Florian Weimer / Red Hat Product Security Team
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