Re: [RFC] CPUMASK: proposal for replacing cpumask_t

From: H. Peter Anvin
Date: Fri Sep 12 2008 - 19:05:55 EST

Mike Travis wrote:

Here's the thread:

It doesn't seem worthwhile to force all systems to deal with large cpumask's
if they don't need to. Passing the value on the stack (actually usually in a
reg) if it fits into a long makes a lot of sense.

And I don't think it's that abstract, but I'm willing to hear other opinions.

Btw, most likely only distros that distribute an "Enterprise" edition of
Linux will ever set NR_CPUS so high, so the actual number of systems making
use of this will be a very small percentage (big $$-wise though... ;-)

I even think that perhaps BITS_PER_LONG might be too low a threshold to kick
in this extra code. A Larabee chip will have 128 cpus so maybe 128 or 256 is
a better metric...?

As soon as I get a working kernel with the proposed changes, I will definitely
be doing perf testing.

If the performance difference isn't significant, then there is a major advantage to getting rid of a configuration option. At that point we can basically scale to an arbitrary number of processors in a stock configuration.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at