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Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread
Date 2016-03-02 11:40 +0100
Message-ID <r8cmd-6mR-9@gated-at.bofh.it> (permalink)
References (5 earlier) <r7aFQ-3MT-5@gated-at.bofh.it> <r7tp9-1NN-37@gated-at.bofh.it> <r7Z5E-5Mg-17@gated-at.bofh.it> <r80bn-6s3-1@gated-at.bofh.it> <r80uK-6zV-9@gated-at.bofh.it>
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On Tue, Mar 01, 2016 at 01:47:38PM -0800, H. Peter Anvin wrote:
> On 03/01/16 13:32, Peter Zijlstra wrote:
> > On Tue, Mar 01, 2016 at 08:23:12PM +0000, Mathieu Desnoyers wrote:
> >> I think it's important that user-space fast-paths can quickly
> >> detect whether the feature is enabled without having to rely on
> >> always reading a separate cache-line. I've put together an ABI
> >> proposal that take into account the feedback received so far.
> > 
> > Nah, adding detectoring code to fast paths is silly, makes them less
> > fast. Doesn't userspace have self modifying code? I know that at least
> > glibc does linker trickery to call different functions depending on
> > runtime context.
> > 
> 
> No, userspace does not have self-modifying code.  The glibc indirect
> function is done at dynamic link time; it is also worth noting that
> resolving global symbols through dynamic linking often requires an
> indirect call.

Boy that blows. And here I was thinking you could edit the code at
dynamic link time because nobody was running it yet :/

And I suppose JITs need an (effective) munmap()+mmap() cycle to ensure
the 'old' code is flushed from all caches etc..?

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[PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-24 00:30 +0100
  Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Thomas Gleixner <tglx@linutronix.de> - 2016-02-24 12:20 +0100
    Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-24 18:20 +0100
    Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-02-26 00:40 +0100
      Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-26 18:50 +0100
  Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-02-25 11:00 +0100
    Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-25 18:00 +0100
      Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-02-25 18:10 +0100
        Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-25 18:20 +0100
          Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-02-26 12:40 +0100
            Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Thomas Gleixner <tglx@linutronix.de> - 2016-02-26 17:40 +0100
              Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-26 18:30 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Thomas Gleixner <tglx@linutronix.de> - 2016-02-26 19:10 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-26 21:30 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread "H. Peter Anvin" <hpa@zytor.com> - 2016-02-27 00:10 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-27 01:50 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread "H. Peter Anvin" <hpa@zytor.com> - 2016-02-27 07:30 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-27 15:20 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-02-27 16:00 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-27 19:40 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread "H. Peter Anvin" <hpa@zytor.com> - 2016-02-27 20:10 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-28 01:00 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-28 02:00 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-28 15:40 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-02-29 11:40 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-03-01 21:30 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-03-01 22:40 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-03-01 22:40 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread "H. Peter Anvin" <hpa@zytor.com> - 2016-03-01 23:00 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-03-02 11:40 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-02-29 11:40 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread Arnd Bergmann <arnd@arndb.de> - 2016-02-29 11:50 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-29 13:50 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread Arnd Bergmann <arnd@arndb.de> - 2016-02-29 14:20 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread "H. Peter Anvin" <hpa@zytor.com> - 2016-02-29 19:30 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Geert Uytterhoeven <geert@linux-m68k.org> - 2016-03-02 11:50 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread "H. Peter Anvin" <hpa@zytor.com> - 2016-03-01 19:30 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-03-01 19:50 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Geert Uytterhoeven <geert@linux-m68k.org> - 2016-02-28 14:10 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-28 17:30 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of  running thread Peter Zijlstra <peterz@infradead.org> - 2016-02-29 11:10 +0100
                Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread "H. Peter Anvin" <hpa@zytor.com> - 2016-02-27 16:10 +0100

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