linux-kernel - Re: [PATCH 10/24] x86/oprofile: Add IBS support for AMD CPUs, IBS buffer handling routines

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Date:	Wed, 23 Jul 2008 21:46:08 +0200
From:	Robert Richter <robert.richter@....com>
To:	Maynard Johnson <maynardj@...ibm.com>
CC:	rrichter@...e.amd.com, Barry Kasindorf <barry.kasindorf@....com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	oprofile-list <oprofile-list@...ts.sourceforge.net>,
	Carl Love <cel@...ibm.com>
Subject: Re: [PATCH 10/24] x86/oprofile: Add IBS support for AMD CPUs, IBS
	buffer handling routines

On 23.07.08 14:20:37, Maynard Johnson wrote:
> Robert Richter wrote:

[...]

> > @@ -252,6 +253,71 @@ void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
> >  	oprofile_add_ext_sample(pc, regs, event, is_kernel);
> >  }
> >
> > +#define MAX_IBS_SAMPLE_SIZE	14
> > +static int log_ibs_sample(struct oprofile_cpu_buffer *cpu_buf,
> > +	unsigned long pc, int is_kernel, unsigned  int *ibs, int ibs_code)
> > +{
> > +	struct task_struct *task;
> > +
> > +	cpu_buf->sample_received++;
> > +
> > +	if (nr_available_slots(cpu_buf) < MAX_IBS_SAMPLE_SIZE) {
> > +		cpu_buf->sample_lost_overflow++;
> > +		return 0;
> > +	}
> > +
> > +	is_kernel = !!is_kernel;
> > +
> > +	/* notice a switch from user->kernel or vice versa */
> > +	if (cpu_buf->last_is_kernel != is_kernel) {
> > +		cpu_buf->last_is_kernel = is_kernel;
> > +		add_code(cpu_buf, is_kernel);
> > +	}
> > +
> > +	/* notice a task switch */
> > +	if (!is_kernel) {
> > +		task = current;
> > +
> > +		if (cpu_buf->last_task != task) {
> > +			cpu_buf->last_task = task;
> > +			add_code(cpu_buf, (unsigned long)task);
> > +		}
> > +	}
> > +
> > +	add_code(cpu_buf, ibs_code);
> > +	add_sample(cpu_buf, ibs[0], ibs[1]);
> > +	add_sample(cpu_buf, ibs[2], ibs[3]);
> > +	add_sample(cpu_buf, ibs[4], ibs[5]);
> > +
> > +	if (ibs_code == IBS_OP_BEGIN) {
> > +	add_sample(cpu_buf, ibs[6], ibs[7]);
> > +	add_sample(cpu_buf, ibs[8], ibs[9]);
> > +	add_sample(cpu_buf, ibs[10], ibs[11]);
> > +	}
> > +
> > +	return 1;
> > +}
> > +
> >   
> I'm concerned about the arch-specific nature of the "ibs" functions
> above being placed here in the generic portion of the oprofile driver. 
> Better to generalize the external function defined below (and rename it)
> by invoking arch-specific handlers via function pointers.  Hopefully
> find a way to move the arch-specific code back to where it belongs,
> under the appropriate arch/ directory.

Yes, this is true. The plan is to rework the code so that IBS is only
in op_model_amd.c. The only thing visible outside will then be the
code macros introduced in patch #9. The code will change into generic
with something like add_u64(). This function will then be called from
the IBS handler.

This is also the reason I did not add op_amd_handle_ibs() to the API
definition in linux/oprofile.h.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center
email: robert.richter@....com

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