Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1319182

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

Show all headers | View raw

----- On Jan 27, 2016, at 12:24 PM, Thomas Gleixner tglx@linutronix.de 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

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[RFC PATCH v2 0/3] getcpu_cache system call Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-01-27 18:00 +0100
  [RFC PATCH v2 3/3] getcpu_cache: wire up x86 32/64 system call Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-01-27 18:00 +0100
  [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-01-27 18:00 +0100
    Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number  of running thread Thomas Gleixner <tglx@linutronix.de> - 2016-01-27 18:30 +0100
      Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number  of running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-01-27 18:40 +0100
        Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of  running thread Josh Triplett <josh@joshtriplett.org> - 2016-01-27 19:10 +0100
          Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number  of running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-01-27 19:50 +0100
            Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of  running thread Josh Triplett <josh@joshtriplett.org> - 2016-01-27 20:40 +0100
              Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number  of running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-01-27 22:10 +0100
                Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of  running thread Josh Triplett <josh@joshtriplett.org> - 2016-01-27 22:40 +0100
        Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of  running thread Andrew Hunter <ahh@google.com> - 2016-01-27 19:10 +0100
    Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number  of running thread Thomas Gleixner <tglx@linutronix.de> - 2016-01-27 18:30 +0100
      Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number  of running thread Thomas Gleixner <tglx@linutronix.de> - 2016-01-27 18:40 +0100
        Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number  of running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-01-27 22:40 +0100
      Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number  of running thread Thomas Gleixner <tglx@linutronix.de> - 2016-01-27 18:40 +0100
      Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number  of running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-01-27 18:40 +0100
    Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of  running thread Josh Triplett <josh@joshtriplett.org> - 2016-01-27 18:30 +0100

csiph-web