From: Peter Zijlstra <peterz@infradead•org>
To: Pan Xinhui <xinhui@linux•vnet.ibm.com>
Cc: linux-kernel@vger•kernel.org, linuxppc-dev@lists•ozlabs.org,
benh@kernel•crashing.org, paulus@samba•org, mpe@ellerman•id.au,
boqun.feng@gmail•com, paulmck@linux•vnet.ibm.com,
tglx@linutronix•de
Subject: Re: [PATCH V3] powerpc: Implement {cmp}xchg for u8 and u16
Date: Wed, 20 Apr 2016 16:24:08 +0200 [thread overview]
Message-ID: <20160420142408.GF3430@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <571782F0.2020201@linux.vnet.ibm.com>
On Wed, Apr 20, 2016 at 09:24:00PM +0800, Pan Xinhui wrote:
> +#define __XCHG_GEN(cmp, type, sfx, skip, v) \
> +static __always_inline unsigned long \
> +__cmpxchg_u32##sfx(v unsigned int *p, unsigned long old, \
> + unsigned long new); \
> +static __always_inline u32 \
> +__##cmp##xchg_##type##sfx(v void *ptr, u32 old, u32 new) \
> +{ \
> + int size = sizeof (type); \
> + int off = (unsigned long)ptr % sizeof(u32); \
> + volatile u32 *p = ptr - off; \
> + int bitoff = BITOFF_CAL(size, off); \
> + u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff; \
> + u32 oldv, newv, tmp; \
> + u32 ret; \
> + oldv = READ_ONCE(*p); \
> + do { \
> + ret = (oldv & bitmask) >> bitoff; \
> + if (skip && ret != old) \
> + break; \
> + newv = (oldv & ~bitmask) | (new << bitoff); \
> + tmp = oldv; \
> + oldv = __cmpxchg_u32##sfx((v u32*)p, oldv, newv); \
> + } while (tmp != oldv); \
> + return ret; \
> +}
So for an LL/SC based arch using cmpxchg() like that is sub-optimal.
Why did you choose to write it entirely in C?
next prev parent reply other threads:[~2016-04-20 14:24 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-19 6:29 [PATCH V2] powerpc: Implement {cmp}xchg for u8 and u16 Pan Xinhui
2016-04-19 9:18 ` Boqun Feng
2016-04-20 3:39 ` Pan Xinhui
2016-04-20 13:24 ` [PATCH V3] " Pan Xinhui
2016-04-20 14:24 ` Peter Zijlstra [this message]
2016-04-21 15:35 ` Pan Xinhui
2016-04-21 15:52 ` Boqun Feng
2016-04-22 1:59 ` Pan Xinhui
2016-04-22 3:16 ` Boqun Feng
2016-04-21 16:13 ` Peter Zijlstra
2016-04-25 10:10 ` Pan Xinhui
2016-04-25 15:37 ` Peter Zijlstra
2016-04-26 11:35 ` Pan Xinhui
2016-04-27 9:16 ` [PATCH V4] " Pan Xinhui
2016-04-27 13:58 ` Boqun Feng
2016-04-27 14:16 ` Boqun Feng
2016-04-27 14:50 ` Boqun Feng
2016-04-27 14:59 ` Boqun Feng
2016-04-28 10:21 ` Pan Xinhui
2016-04-28 7:59 ` Peter Zijlstra
2016-04-28 10:21 ` Pan Xinhui
2016-11-25 0:04 ` [V4] " Michael Ellerman
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