Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable

From	"H. Peter Anvin" <hpa@zytor.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable
Date	2016-04-21 00:40 +0200
Message-ID	<rq8WS-75x-11@gated-at.bofh.it> (permalink)
References	(6 earlier) <rq0FY-fr-19@gated-at.bofh.it> <rq4JC-3Ai-49@gated-at.bofh.it> <rq7eq-5Ab-9@gated-at.bofh.it> <rq7xM-64O-7@gated-at.bofh.it> <rq80O-6j3-9@gated-at.bofh.it>
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On April 20, 2016 2:36:37 PM PDT, Borislav Petkov <bp@alien8.de> wrote:
>On Wed, Apr 20, 2016 at 02:06:33PM -0700, H. Peter Anvin wrote:
>> Setting ret to sem doesn't make any sense.  Just use "=a" and "a".
>
>Yeah, that's what Michal's patch ontop does.
>
>And to answer my own question: we need the "a" (sem) input for the fast
>path.
>
>I guess we can still move "1" (RWSEM_ACTIVE_WRITE_BIAS) before the
>asm():
>
>	long tmp = RWSEM_ACTIVE_WRITE_BIAS;
>
>One thing I'm still not clear on is why we need the output tmp operand:
>"=d" (tmp) ?

Since it is a fixed register we could just mark edx clobbered, but with more flexible register constraints it can permit gcc to allocate a temp resister for us.
-- 
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Thread

Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Peter Zijlstra <peterz@infradead.org> - 2016-04-20 15:50 +0200
  Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable "H. Peter Anvin" <hpa@zytor.com> - 2016-04-20 20:10 +0200
    Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Borislav Petkov <bp@alien8.de> - 2016-04-20 22:50 +0200
      Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Michal Hocko <mhocko@kernel.org> - 2016-04-20 23:00 +0200
      Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable "H. Peter Anvin" <hpa@zytor.com> - 2016-04-20 23:10 +0200
        Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Borislav Petkov <bp@alien8.de> - 2016-04-20 23:40 +0200
          Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable "H. Peter Anvin" <hpa@zytor.com> - 2016-04-21 00:40 +0200
            Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Borislav Petkov <bp@alien8.de> - 2016-04-21 13:40 +0200
              Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Michal Hocko <mhocko@kernel.org> - 2016-04-21 15:10 +0200
                Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Borislav Petkov <bp@alien8.de> - 2016-04-21 15:30 +0200
            [PATCH] x86/locking/rwsem: Cleanup ____down_write() Borislav Petkov <bp@alien8.de> - 2016-04-27 14:10 +0200
              [tip:locking/rwsem] locking/rwsem, x86: Clean up ____down_write() tip-bot for Borislav Petkov <tipbot@zytor.com> - 2016-04-28 12:30 +0200
  Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Ingo Molnar <mingo@kernel.org> - 2016-04-22 09:00 +0200

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