Messages in this thread | | | From | (Linus Torvalds) | Subject | Re: Locking L1 cache lines in Cyrix 6x86MX CPUs | Date | 20 May 1998 05:29:50 GMT |
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In article <199805192329.TAA02841@tiktok.cygnus.com>, Michael Meissner <meissner@cygnus.com> wrote: > >Obviously to use this, you will need to rebuild all of your favorite apps >(unless you are talking kernel only) with your special compiler option. You >also need to have the context code swap these values as well. > >I am skeptical it will provide much benefit.
Also note that locking down cache lines is almost never a win anyway, unless you have some _very_ specific uses for the machine.
For example, even if we locked down a very commonly used line in the kernel, what would happen to all those applications that are running almost totally in user mode? To them, the cache would appear smaller than it would otherwise be.
Locking down the cache line is usually worth it only if:
- you have a very specialized application or use for the CPU, and you _know_ that something is always so important that it really is worth it.
or
- you have real-time constraints that you cannot guarantee any other way. You know that locking down the cache may be bad for overall performance, but at least you'll get _repeatable_ performance or some particular routine has such strict latency requirements that you don't care that you're slowing down everything else.
So I applaud the larger cache in the Cyrix CPU, but I suspect it is better used as a regular cache rather than anything else. It's not as if a 64kB L1 is excessive these days - there are rather few applications that wouldn't be happier with more. Often quite a lot more.
Linus
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