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From: Noah Goldstein <>
To: Wilco Dijkstra <>
Cc: GNU C Library <>
Subject: Re: [PATCH v1 2/4] nptl: Continue use arch prefered atomic exchange in spinlock loop
Date: Thu, 29 Sep 2022 11:38:56 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Thu, Sep 29, 2022 at 9:35 AM Wilco Dijkstra <> wrote:
> Hi Noah,
> Did you try building it both ways? I don't think this could ever compile:
> +  if (__glibc_likely (pthread_spin_lock_grab_lock (lock, &val, 1)))
> and:
> +#  define pthread_spin_lock_grab_lock(mem, val, c) \
> +    atomic_compare_exchange_weak_acquire (lock, &val, 1))
> The define uses 'lock' and 'mem' inconsistently and the use of the macro
> expands into &&val...
> Apart from that there is the question whether we should keep the weird
> ATOMIC_EXCHANGE_USES_CAS setting - I have removed it in my atomic
> patch series since most targets appear confused as to what it means (so
> are likely to have the wrong setting). Also there is no evidence it is actually
> faster. So using exchange in both cases is easier (and less error prone!).
> Also you do realize that no matter how much you change this code, it
> won't make a difference on x86, right?

Why's that?
> Cheers,
> Wilco

  reply	other threads:[~2022-09-29 18:39 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-29 16:35 Wilco Dijkstra
2022-09-29 18:38 ` Noah Goldstein [this message]
2022-09-29 18:50   ` Wilco Dijkstra
2022-09-29 18:51   ` H.J. Lu
  -- strict thread matches above, loose matches on Subject: below --
2022-09-29  3:14 [PATCH v1 1/4] Benchtests: Add benchtests for pthread_spin_lock and mutex_trylock Noah Goldstein
2022-09-29  3:14 ` [PATCH v1 2/4] nptl: Continue use arch prefered atomic exchange in spinlock loop Noah Goldstein

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