Linus Torvalds wrote:
> A hot system call takes about 0.2 us on an athlon (it takes significantly
> longer on a P4, which I'm beating up Intel over all the time). The ioctl
> stuff goes through slightly more layers, but we're not talking huge
> numbers here. The system calls are fast enough that you're better off
> trying to keep stuff in the cache, than trying to minimize system calls.
This is an education for me, too. Thanks for the info. Any idea how
heavy IOCTL's are on a P4?
> NOTE NOTE NOTE! The tradeoffs are seldom all that clear. Sometimes big
> buffers and few system calls are better. Sometimes they aren't. It just
> depends on a lot of things.
You bet--and the real issue we're constantly swimming up stream against
is "security" in open source. Most hardware vendors design the hardware
for closed source drivers and don't put many (or sometimes any) time
into making sure their hardware is optimized for performance *and*
security. Consequently most modern graphics chips are optimized for
user space DMA and they rely on security through obscurity of their
closed source drivers. Then, the DRI team comes along and has to figure
out how to kludge together a secure path that doesn't sacrafice *all*
the performance.
Linus, if you have any ideas on how we can uphold the security strengths
of Linux without leaving all this performance on the table simply
because we embrace open source, then I'd love to hear it. It really
hurts to be competing tooth and nail against closed source drivers (on
Linux even) and have to leave potentially large performance gains on the
table.
The other paradox here is that security is paramount for the server
market where Linux is strong. But we're trying to help Linux into the
domain of the graphics workstation and game machine markets where users
already have full access to the machine (even physically). So how is
all this security really helping us address those market?
Sorry, I'm venting. This has been a difficult issue since the beginning
of the DRI project--but I'm glad I got it off my chest :-)
Regards,
Jens
-- /\
Jens Owen / \/\ _
[EMAIL PROTECTED] / \ \ \ Steamboat Springs, Colorado
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