linux-kernel - Re: [PATCH 12/29] x86, tsx: Add a per thread transaction disable count

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Date:	Sat, 23 Mar 2013 12:51:15 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, x86@...nel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 12/29] x86, tsx: Add a per thread transaction disable
 count

On Fri, Mar 22, 2013 at 06:25:06PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> For some locks that have a low chance of not aborting it's
> best to just disable transactions.
> 
> Add a counter to thread_info to allow to disable tranasctions
> for the current task.
> 
> I originally experimented with more complicated solutions,
> like a magic spinlock type to disable with magic type matching,
> but that was very intrusive in the locking code.
> 
> This setup -- while adding a few more instructions -- is more
> flexible and seems to work quite nicely.
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  arch/x86/include/asm/thread_info.h |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
> index 2cd056e..91bb84e 100644
> --- a/arch/x86/include/asm/thread_info.h
> +++ b/arch/x86/include/asm/thread_info.h
> @@ -39,6 +39,7 @@ struct thread_info {
>  						*/
>  	__u8			supervisor_stack[0];
>  #endif
> +	unsigned		notxn;		/* transactions are disabled */

This surely can be a bitfield like the other two below. It is basically
begging to be one.

>  	unsigned int		sig_on_uaccess_error:1;
>  	unsigned int		uaccess_err:1;	/* uaccess failed */
>  };

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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