I am having a performance problem with a blocking Posix serial thread.
- My Posix serial thread is designed to QUICKLY reply to an incoming
serial message. it blocks waiting for the start of the incoming
message, then reads the remainder when it wakes, and quickly replies.
- At any time there can be an extremely heavy load on the attached
storage (SATA or SAN), since the application is dealing with Video
material.
- We observe that the ability for our Posix serial thread to reply
_promptly_ is compromised by the load on the storage - ie. if the
storage is being hit hard, at the same time the serial message is
coming in, our thread seems to be delayed somewhat, by a matter of
10mSecs or more.
I have experimented with thread priority, and setting the thread to
realtime, but nothing seems to help. Using XSan seems to make the
problem worse than using local SATA storage.
The problem is worse at the point when video playback starts, and
there is a massive rush on the storage.
Its not clear exactly where the holdup is. I guess its possible that
the serial driver is being held up rather than my thread itself -
perhaps delaying the incoming bytes, or the outgoing reply.
Can anyone advise how to raise my thread's status above that of the
storage subsystem ? Any other tips for no-compromise performance on
my thread (the thread doesn't do very much, but it needs to respond
very quickly to the incoming data).
