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Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of failed SCOND with exponential backoff

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of failed SCOND with exponential backoff
Date 2015-08-03 16:10 +0200
Message-ID <pToBb-5iK-7@gated-at.bofh.it> (permalink)
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On Mon, Aug 03, 2015 at 01:50:01PM +0000, Vineet Gupta wrote:
> diff --git a/arch/arc/include/asm/atomic.h b/arch/arc/include/asm/atomic.h
> index 3dd36c1efee1..c2e012ca4560 100644
> --- a/arch/arc/include/asm/atomic.h
> +++ b/arch/arc/include/asm/atomic.h
> @@ -23,17 +23,50 @@
>  
>  #define atomic_set(v, i) (((v)->counter) = (i))
>  
> +#ifdef CONFIG_ARC_STAR_9000923308
> +
> +#define SCOND_FAIL_RETRY_VAR_DEF                        \
> +    unsigned int delay = 1, tmp;                        \
> +
> +#define SCOND_FAIL_RETRY_ASM                            \
> +    "    bz    4f            \n"                \
> +    "   ; --- scond fail delay ---        \n"                \
> +    "    mov    %[tmp], %[delay]    \n"    /* tmp = delay */    \
> +    "2:     brne.d    %[tmp], 0, 2b        \n"    /* while (tmp != 0) */    \
> +    "    sub    %[tmp], %[tmp], 1    \n"    /* tmp-- */        \
> +    "    asl    %[delay], %[delay], 1    \n"    /* delay *= 2 */    \

You forgot the overflow test .. :-)

> +    "    b    1b            \n"    /* start over */    \
> +    "4: ; --- success ---            \n"                \
> +
> +#define SCOND_FAIL_RETRY_VARS                            \
> +      ,[delay] "+&r" (delay),[tmp] "=&r"    (tmp)                \
> +
> +#else    /* !CONFIG_ARC_STAR_9000923308 */
> +
> +#define SCOND_FAIL_RETRY_VAR_DEF
> +
> +#define SCOND_FAIL_RETRY_ASM                            \
> +    "    bnz     1b            \n"                \
> +
> +#define SCOND_FAIL_RETRY_VARS
> +
> +#endif

But yes, much better.
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[PATCH 0/6] ARC: spinlocks/atomics rework Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 12:10 +0200
  [PATCH 4/6] ARC: LLOCK/SCOND based rwlock Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 12:10 +0200
    Re: [PATCH 4/6] ARC: LLOCK/SCOND based rwlock Peter Zijlstra <peterz@infradead.org> - 2015-08-03 13:40 +0200
      Re: [PATCH 4/6] ARC: LLOCK/SCOND based rwlock Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 14:00 +0200
  [PATCH 6/6] ARCv2: spinlock/rwlock: Reset retry delay when starting a new spin-wait cycle Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 12:10 +0200
    Re: [PATCH 6/6] ARCv2: spinlock/rwlock: Reset retry delay when  starting a new spin-wait cycle Peter Zijlstra <peterz@infradead.org> - 2015-08-03 13:50 +0200
      Re: [PATCH 6/6] ARCv2: spinlock/rwlock: Reset retry delay when  starting a new spin-wait cycle Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 16:50 +0200
        Re: [PATCH 6/6] ARCv2: spinlock/rwlock: Reset retry delay when  starting a new spin-wait cycle Peter Zijlstra <peterz@infradead.org> - 2015-08-03 16:50 +0200
  [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of failed SCOND with exponential backoff Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 12:10 +0200
    Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of  failed SCOND with exponential backoff Peter Zijlstra <peterz@infradead.org> - 2015-08-03 13:50 +0200
      Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of  failed SCOND with exponential backoff Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 15:10 +0200
        Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of  failed SCOND with exponential backoff Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 16:00 +0200
          Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of  failed SCOND with exponential backoff Peter Zijlstra <peterz@infradead.org> - 2015-08-03 16:10 +0200
    Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of  failed SCOND with exponential backoff Peter Zijlstra <peterz@infradead.org> - 2015-08-03 14:00 +0200
      Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of  failed SCOND with exponential backoff Peter Zijlstra <peterz@infradead.org> - 2015-08-03 15:10 +0200
      Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of  failed SCOND with exponential backoff Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 15:10 +0200
  [PATCH 3/6] ARC: LLOCK/SCOND based spin_lock Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 12:10 +0200
    Re: [PATCH 3/6] ARC: LLOCK/SCOND based spin_lock Peter Zijlstra <peterz@infradead.org> - 2015-08-03 13:30 +0200
      Re: [PATCH 3/6] ARC: LLOCK/SCOND based spin_lock Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 13:50 +0200
  [PATCH 1/6] Revert "ARCv2: STAR 9000837815 workaround hardware exclusive transactions livelock" Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 12:10 +0200
  [PATCH 2/6] ARC: refactor atomic inline asm operands with symbolic names Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-03 12:10 +0200

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