Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of running thread

[Mathieu Desnoyers]

----- On Jan 27, 2016, at 12:24 PM, Thomas Gleixner tglx@xxxxxxxxxxxxx wrote:

> On Wed, 27 Jan 2016, Josh Triplett wrote:
>> With the dynamic allocation removed, this seems sensible to me.  One
>> minor nit: s/int32_t/uint32_t/g, since a location intended to hold a CPU
>> number should never need to hold a negative number.
> 
> You try to block the future of computing: https://lwn.net/Articles/638673/

Besides impossible architectures, there is actually a use-case for
signedness here. It makes it possible to initialize the cpu number
cache to a negative value, e.g. -1, in userspace. Then, a check for
value < 0 can be used to figure out cases where the getcpu_cache
system call is not implemented, and where a fallback (vdso or getcpu
syscall) needs to be used.

This is why I have chosen a signed type for the cpu cache so far.

Thoughts ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com