linux-kernel - Re: [PATCH 04/20] x86/ticketlock: make large and small ticket versions of spin

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Message-ID: <20101112121932.GA30016@linux.vnet.ibm.com>
Date:	Fri, 12 Nov 2010 17:49:32 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.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>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 04/20] x86/ticketlock: make large and small ticket
 versions of spin_lock the same

On Wed, Nov 03, 2010 at 10:59:45AM -0400, Jeremy Fitzhardinge wrote:
> Make the bulk of __ticket_spin_lock look identical for large and small
> number of cpus.

[snip]

>  #if (NR_CPUS < 256)
>  static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
>  {
> -	register union {
> -		struct __raw_tickets tickets;
> -		unsigned short slock;
> -	} inc = { .slock = 1 << TICKET_SHIFT };
> +	register struct __raw_tickets inc = { .tail = 1 };

[snip]

>  #else
>  static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
>  {
> -	unsigned inc = 1 << TICKET_SHIFT;
> -	__ticket_t tmp;
> +	register struct __raw_tickets inc = { .tickets.tail = 1 };

s/.tickets//?

Otherwise I get a compile error for NR_CPUS > 256, with just 4 patches applied.

- vatsa
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