linux-kernel - Re: [patch 05/24] perfmon: X86 generic code (x86)

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Message-ID: <20081126140054.GX6703@one.firstfloor.org>
Date:	Wed, 26 Nov 2008 15:00:54 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	eranian@...glemail.com, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mingo@...e.hu, x86@...nel.org,
	andi@...stfloor.org, eranian@...il.com, sfr@...b.auug.org.au
Subject: Re: [patch 05/24] perfmon: X86 generic code (x86)

On Wed, Nov 26, 2008 at 02:35:18PM +0100, Thomas Gleixner wrote:
> > +	 * 	  does not work with other types of PMU registers.Thus, no
> > +	 * 	  address is ever exposed by counters
> > +	 *
> > +	 * 	- there is never a dependency between one pmd register and
> > +	 * 	  another
> > +	 */
> > +	for (i = 0; num; i++) {
> > +		if (likely(pfm_arch_bv_test_bit(i, set->used_pmds))) {
> > +			pfm_write_pmd(ctx, i, set->pmds[i]);
> > +			num--;
> > +		}
> > +	}
> 
>   This loop construct looks scary. It relies on set->nused_pmds >=
>   bits set in set->used_pmds. I had to look more than once to
>   understand that. It's used all over the code in variations.

FWIW this loop style tripped me up during review too.

> > +	 */
> > +	pfm_arch_resend_irq(ctx);
> 
> Do we really need this whole NMI business ?

Without it you cannot profile interrupts off regions well.

> 
> 9 simple wrappers around generic bitops. The only reason you need
> those is because you use 64bit variables and that does not work on
> 32bit BE machines.
> 
> I do not understand in the first place why you cant use simple
> unsigned longs for the bitfields, but if this is necessary for
> whatever non obvious reason, then its not an excuse to make this arch
> dependent code at all. You need a LE/BE64 and a BE32 version.  So you
> need a generic and a special be32 version. That's not arch specific.

Or a unsigned long x[VALUE_DEPENDS_ON_WORD_SIZE]

-Andi
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