The contextmanager eventlet.timeout.Timeout is scheduling a call to
throw an exception every time is is entered. The swift-proxy uses
Chunk(Read|Write)Timeout for every chunk read/written from the client or
object-server. For a single upload/download of a big object, it means
tens of thousands of scheduling in eventlet, which is very costly.
This patch replace the usage of these context managers by a watchdog
greenthread that will schedule itself by sleeping until the next timeout
expiration. Then, only if a timeout expired, it will schedule a call to
throw the appropriate exception.
The gain on bandwidth and CPU usage is significant. On a benchmark
environment, it gave this result for an upload of 6 Gbpson a replica
policy (average of 3 runs):
master: 5.66 Gbps / 849 jiffies consumed by the proxy-server
this patch: 7.56 Gbps / 618 jiffies consumed by the proxy-server
Change-Id: I19fd42908be5a6ac5905ba193967cd860cb27a0b
8378a11d11