Groups > linux.kernel > #1191170

Re: Kernel broken on processors without performance counters

From	Jason Baron <jasonbaron0@gmail.com>
Newsgroups	linux.kernel
Subject	Re: Kernel broken on processors without performance counters
Date	2015-07-23 19:40 +0200
Message-ID	<pPsDo-578-1@gated-at.bofh.it> (permalink)
References	(6 earlier) <pOTPj-4tw-5@gated-at.bofh.it> <pP5GO-5fE-11@gated-at.bofh.it> <pPmeC-4gU-19@gated-at.bofh.it> <pPqLg-2oy-19@gated-at.bofh.it> <pPsam-4z3-25@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 07/23/2015 01:08 PM, Peter Zijlstra wrote:
> On Thu, Jul 23, 2015 at 11:34:50AM -0400, Steven Rostedt wrote:
>> On Thu, 23 Jul 2015 12:42:15 +0200
>> Peter Zijlstra <peterz@infradead.org> wrote:
>>
>>> static __always_inline bool arch_static_branch_jump(struct static_key *key, bool inv)
>>> {
>>> 	if (!inv) {
>>> 		asm_volatile_goto("1:"
>>> 			"jmp %l[l_yes]\n\t"
>> And what happens when this gets converted to a two byte jump?
>>
> That would be bad, how can we force it to emit 5 bytes?
hmm....I don't think that's an issue, the patching code can
detect if its a 2-byte jump - 0xeb, or 5-byte: 0xe9, and do
the correct no-op. Same going the other way. See the code
I posted a few mails back. In fact, this gets us to the
smaller 2-byte no-ops in cases where we are initialized
to jump.

Thanks,

-Jason
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Thread

Re: Kernel broken on processors without performance counters Jason Baron <jasonbaron0@gmail.com> - 2015-07-22 19:10 +0200
  Re: Kernel broken on processors without performance counters Peter Zijlstra <peterz@infradead.org> - 2015-07-23 19:10 +0200
    Re: Kernel broken on processors without performance counters Steven Rostedt <rostedt@goodmis.org> - 2015-07-23 19:20 +0200
    Re: Kernel broken on processors without performance counters Jason Baron <jasonbaron0@gmail.com> - 2015-07-23 19:40 +0200
      Re: Kernel broken on processors without performance counters Steven Rostedt <rostedt@goodmis.org> - 2015-07-23 20:20 +0200
      Re: Kernel broken on processors without performance counters Peter Zijlstra <peterz@infradead.org> - 2015-07-23 21:10 +0200
    Re: Kernel broken on processors without performance counters Andy Lutomirski <luto@amacapital.net> - 2015-07-23 19:40 +0200
    Re: Kernel broken on processors without performance counters Borislav Petkov <bp@alien8.de> - 2015-07-23 20:00 +0200
      Re: Kernel broken on processors without performance counters Peter Zijlstra <peterz@infradead.org> - 2015-07-23 21:10 +0200
        Re: Kernel broken on processors without performance counters Peter Zijlstra <peterz@infradead.org> - 2015-07-24 12:40 +0200
  Re: Kernel broken on processors without performance counters Peter Zijlstra <peterz@infradead.org> - 2015-07-24 13:00 +0200
    Re: Kernel broken on processors without performance counters Peter Zijlstra <peterz@infradead.org> - 2015-07-24 14:40 +0200
      Re: Kernel broken on processors without performance counters Jason Baron <jasonbaron0@gmail.com> - 2015-07-24 16:20 +0200

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