Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

Ilpo Järvinen wrote:

On Thu, 16 Aug 2007, Herbert Xu wrote:

We've been through that already.  If it's a busy-wait it

should use cpu_relax.

I looked around a bit by using some command lines and ended up wondering if these are equal to busy-wait case (and should be fixed) or not:

./drivers/telephony/ixj.c
6674:   while (atomic_read(&j->DSPWrite) > 0)
6675-           atomic_dec(&j->DSPWrite);

...besides that, there are couple of more similar cases in the same file (with braces)...

atomic_dec() already has volatile behavior everywhere, so this is semantically okay, but this code (and any like it) should be calling cpu_relax() each iteration through the loop, unless there's a compelling reason not to. I'll allow that for some hardware drivers (possibly this one) such a compelling reason may exist, but hardware-independent core subsystems probably have no excuse.

If the maintainer of this code doesn't see a compelling reason not to add cpu_relax() in this loop, then it should be patched.

	-- Chris
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• References:
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: "Paul E. McKenney" <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Christoph Lameter <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Paul Mackerras <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Herbert Xu <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Paul Mackerras <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Satyam Sharma <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Satyam Sharma <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Paul Mackerras <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Herbert Xu <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Paul Mackerras <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: Herbert Xu <[email protected]>
  • Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
    • From: "Ilpo Järvinen" <[email protected]>

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