linux-kernel - Re: [PATCH 01/20] x86/ticketlock: clean up types and accessors

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Message-ID: <20101113095732.GF3837@hack>
Date:	Sat, 13 Nov 2010 17:57:32 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Jan Beulich <JBeulich@...ell.com>, Avi Kivity <avi@...hat.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 01/20] x86/ticketlock: clean up types and accessors

On Wed, Nov 03, 2010 at 10:59:42AM -0400, Jeremy Fitzhardinge wrote:
...
> static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
> {
>-	int inc = 0x00010000;
>-	int tmp;
>+	unsigned inc = 1 << TICKET_SHIFT;
>+	unsigned tmp;

Please don't use old implicit-int.

> 
>-	return (((tmp >> TICKET_SHIFT) - tmp) & ((1 << TICKET_SHIFT) - 1)) > 1;
>+	return ((tmp.tail - tmp.head) & TICKET_MASK) > 1;


There is a type promotion here.


> }
> 
> #ifndef CONFIG_PARAVIRT_SPINLOCKS
>diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
>index dcb48b2..4582640 100644
>--- a/arch/x86/include/asm/spinlock_types.h
>+++ b/arch/x86/include/asm/spinlock_types.h
>@@ -5,11 +5,27 @@
> # error "please don't include this file directly"
> #endif
> 
>+#include <linux/types.h>
>+
>+#if (CONFIG_NR_CPUS < 256)
>+typedef u8  __ticket_t;
>+#else
>+typedef u16 __ticket_t;
>+#endif
>+
>+#define TICKET_SHIFT	(sizeof(__ticket_t) * 8)
>+#define TICKET_MASK	((1 << TICKET_SHIFT) - 1)


So here you may need to cast the result to __ticket_t.


Thanks.
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