linux-kernel - Re: [patch 01/11] Introducing generic hardware breakpoint handler interfaces

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Message-ID: <20090310135018.GB3850@elte.hu>
Date:	Tue, 10 Mar 2009 14:50:18 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	prasad@...ux.vnet.ibm.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [patch 01/11] Introducing generic hardware breakpoint handler
	interfaces

* prasad@...ux.vnet.ibm.com <prasad@...ux.vnet.ibm.com> wrote:

> +static u8			tprio[HB_NUM];	/* Thread bp max priorities */
> +LIST_HEAD(kernel_bps);			/* Kernel breakpoint list */
> +static LIST_HEAD(thread_list);			/* thread_hw_breakpoint list */
> +DEFINE_PER_CPU(struct cpu_hw_breakpoint, cpu_bp);

hm, why do we need the whole 'priority' mechanism? It seems very 
over-designed to me.

The likelyhood of both user-space and kernel-space to use 
hw-breakpoints is very low to begin with. And if they use them, 
the likelyhood of there being more than 4 debugregs required in 
the same context is even lower.

If that happens we shouldnt try to be too smart about them - 
just override user-space ones with kernel space ones and that's 
it. No explicit priorities are needed.

	Ingo
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