Greg Weeks (firstname.lastname@example.org) writes:
> What's the performance hit for doing a pref on a cache line that is
> already pref'd? Does it turn into a nop, or do we get some horrible
> degenerate case?
The specification for the prefetch instruction is fairly wide, to
permit different implementations to act differently. It's perfectly
legal for it to be a no-op. However, implementors are told that they
should not do anything which would make performance *worse* than if it
was a no-op.
> Are 64 bit processors always at least 32 byte cache line size?
There's no reliable correlation. If you were to go round the
"autogenerated at kernel-startup-time" route, then you can figure out
the line size from the "Config" registers (MIPS32- or MIPS64-compliant
CPUs) or from a table of CPU IDs or otherwise (earlier CPUs)...