Re: Summary: Preventing Transfer Delay to DR-11

From: Guy Harris (guy@Auspex.COM)
Date: Thu May 07 1992 - 16:25:49 CDT

>It's worth noting that SunOS 4.0.3 does not have Shared Objects/Libs,
>thus despite the fact that we had only 8MB of RAM, we had no problems
>with swapping. I claimed 5 buffers of 128MB of shared memory for this

It's worth noting that he presumably means that 4.0.3 *DOES* have shared
objects/libs, because it definitely does....

>If you run set-uid-to-root, you can do more, such as:


> - use asynchronous I/O.

There doesn't appear to be any code in "aioread()" or "aiowrite()" or
anything it calls that *requires* super-user privileges to do
asynchronous I/O, so it's not clear why it requires that the program run
set-UID to "root", if "asynchronous I/O" means "aioread()",
"aiowrite()", and company. In fact, it *doesn't* require super-user

You *do*, of course, have to configure async I/O into the system, if
that's what he meant by "asynchronous I/O".

> This is the biggest potential win, the
> driver has to allow setting up the pending DMA and switching
> to it at interrupt time. That would shorten latency to ~30 microsec.

With the "aioread()"-and-company async I/O, the driver hasn't any idea
that async I/O is being done; it's done by handing the I/O request to a
kernel thread which does the request as an ordinary synchronous I/O

Now, if you're referring to modifying the driver to do async I/O itself,
yes, that'd probably require root privileges, so that you can reboot the
machine with the kernel with the new driver, or load the new driver with

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