Re: transactions in Vino

Chris Small (chris@research.bell-labs.com)
Tue, 22 Jun 1999 15:38:05 -0400 (EDT)


A transaction is wrapped around every extension invocation, not every
kernel operation; the overhead seen depends on how many extensions are
in the path of the operation.

The L4 IPC overhead is an interesting figure, but I'm not sure how it
applies here. What kernel operations are you concerned with? How long
do they take? Is a naked IPC the best benchmark for such an operation?
A getpid()? How about a call to read(), for one byte, when the data is
in the buffer cache? I would guess that on most systems the latter
takes more than 1570 cycles, but a getpid() can be done in the same
amount of time that an L4 IPC can be done.

Once again, this is orthogonal to the main line of discussion; I'm
picking nits.

And of course, no offense taken -- I just wanted to make sure you had
the up-to-date numbers.

- Chris

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