linux-kernel - Re: [PATCH 5/7] hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events

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Date:	Mon, 16 Nov 2009 19:58:11 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jan Kiszka <jan.kiszka@....de>,
	Jiri Slaby <jirislaby@...il.com>, Avi Kivity <avi@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Mike Galbraith <efault@....de>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH 5/7] hw-breakpoints: Rewrite the hw-breakpoints layer on
	top of perf events

On Thu, Nov 12, 2009 at 04:19:52PM +0100, Frederic Weisbecker wrote:
> On Sun, Nov 08, 2009 at 11:01:07PM +0530, K.Prasad wrote:
> > 
> > A few more observations....
> > 
> > int reserve_bp_slot(struct perf_event *bp)
> > {
> > ...
> > ....
> > 	if (!bp->attr.pinned) {
> > 		/*
> > 		 * If there are already flexible counters here,
> > 		 * there is at least one slot reserved for all
> > 		 * of them. Just join the party.
> > 		 *
> > 		 * Otherwise, check there is at least one free slot
> > 		 */
> > 		if (!slots.flexible && slots.pinned == HBP_NUM) {
> > 			ret = -ENOSPC;
> > 			goto end;
> > 		}
> > 
> > 	/* Flexible counters need to keep at least one slot */
> > 	} else if (slots.pinned + (!!slots.flexible) == HBP_NUM) {
> > 		ret = -ENOSPC;
> > 		goto end;
> > 	}
> > ..
> > ...
> > }
> > 
> > It appears that you're reserving one slot for the non-pinned breakpoint
> > requests, which I'm afraid wouldn't play well with PPC64 (having one
> > DABR).
> 
> I don't understand what you mean. PPC64 has only one DABR, or...?
> 

Yes, PPC64 has just one DABR. And so this scheme will allow the first
request (be it 'pinned' or 'unpinned') to use the debug register? Sounds
fine.

Thanks,
K.Prasad

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