From: "Michal Suchánek" <msuchanek@suse.de>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: npiggin@gmail.com, Davidlohr Bueso <dbueso@suse.de>,
peterz@infradead.org, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org, mingo@redhat.com, paulus@samba.org,
longman@redhat.com, will@kernel.org
Subject: Re: [PATCH 3/3] powerpc/qspinlock: Use generic smp_cond_load_relaxed
Date: Tue, 9 Mar 2021 10:39:12 +0100 [thread overview]
Message-ID: <20210309093912.GW6564@kitsune.suse.cz> (raw)
In-Reply-To: <20210309015950.27688-4-dave@stgolabs.net>
On Mon, Mar 08, 2021 at 05:59:50PM -0800, Davidlohr Bueso wrote:
> 49a7d46a06c3 (powerpc: Implement smp_cond_load_relaxed()) added
> busy-waiting pausing with a preferred SMT priority pattern, lowering
> the priority (reducing decode cycles) during the whole loop slowpath.
>
> However, data shows that while this pattern works well with simple
^^^^^^^^^^^^^^^^^^^^^^
> spinlocks, queued spinlocks benefit more being kept in medium priority,
> with a cpu_relax() instead, being a low+medium combo on powerpc.
...
>
> diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
> index aecfde829d5d..7ae29cfb06c0 100644
> --- a/arch/powerpc/include/asm/barrier.h
> +++ b/arch/powerpc/include/asm/barrier.h
> @@ -80,22 +80,6 @@ do { \
> ___p1; \
> })
>
> -#ifdef CONFIG_PPC64
Maybe it should be kept for the simple spinlock case then?
Thanks
Michal
> -#define smp_cond_load_relaxed(ptr, cond_expr) ({ \
> - typeof(ptr) __PTR = (ptr); \
> - __unqual_scalar_typeof(*ptr) VAL; \
> - VAL = READ_ONCE(*__PTR); \
> - if (unlikely(!(cond_expr))) { \
> - spin_begin(); \
> - do { \
> - VAL = READ_ONCE(*__PTR); \
> - } while (!(cond_expr)); \
> - spin_end(); \
> - } \
> - (typeof(*ptr))VAL; \
> -})
> -#endif
> -
> #ifdef CONFIG_PPC_BOOK3S_64
> #define NOSPEC_BARRIER_SLOT nop
> #elif defined(CONFIG_PPC_FSL_BOOK3E)
> --
> 2.26.2
>
next prev parent reply other threads:[~2021-03-09 9:40 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-09 1:59 [PATCH 0/3] powerpc/qspinlock: Some tuning updates Davidlohr Bueso
2021-03-09 1:59 ` [PATCH 1/3] powerpc/spinlock: Define smp_mb__after_spinlock only once Davidlohr Bueso
2021-03-09 1:59 ` [PATCH 2/3] powerpc/spinlock: Unserialize spin_is_locked Davidlohr Bueso
2021-03-09 1:59 ` [PATCH 3/3] powerpc/qspinlock: Use generic smp_cond_load_relaxed Davidlohr Bueso
2021-03-09 9:39 ` Michal Suchánek [this message]
2021-03-09 15:46 ` Davidlohr Bueso
2021-03-09 17:30 ` Michal Suchánek
2021-03-16 4:59 ` Nicholas Piggin
2021-03-18 20:02 ` Davidlohr Bueso
2021-03-18 20:47 ` [PATCH v2] " Davidlohr Bueso
2021-03-31 1:09 ` [PATCH 0/3] powerpc/qspinlock: Some tuning updates Michael Ellerman
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