linux-kernel - Re: [RFC][PATCH 10/14] x86: generic aperf/mperf code.

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Message-Id: <1252075327.8976.3.camel@laptop>
Date:	Fri, 04 Sep 2009 16:42:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dave Jones <davej@...hat.com>
Cc:	Thomas Renninger <trenn@...e.de>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Gautham R Shenoy <ego@...ibm.com>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Balbir Singh <balbir@...ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Yanmin <yanmin_zhang@...ux.intel.com>,
	Len Brown <len.brown@...el.com>,
	Yinghai Lu <yhlu.kernel@...il.com>, cpufreq@...r.kernel.org
Subject: Re: [RFC][PATCH 10/14] x86: generic aperf/mperf code.

On Fri, 2009-09-04 at 10:22 -0400, Dave Jones wrote:
> On Fri, Sep 04, 2009 at 11:27:19AM +0200, Peter Zijlstra wrote:
>  > On Fri, 2009-09-04 at 11:25 +0200, Peter Zijlstra wrote:
>  > > On Fri, 2009-09-04 at 11:19 +0200, Thomas Renninger wrote:
>  > > > You still use struct perf_pair split/hi/lo members in #ifdef __i386__ 
>  > > > case which you deleted above.
>  > > 
>  > > > >               shift_count = fls(h);
>  > > > >  
>  > > > > -             cur.aperf.whole >>= shift_count;
>  > > > > -             cur.mperf.whole >>= shift_count;
>  > > > > +             cur.aperf >>= shift_count;
>  > > > > +             cur.mperf >>= shift_count;
>  > > > >       }
>  > > > >  
>  > > > >       if (((unsigned long)(-1) / 100) < cur.aperf.split.lo) {
>  > > > Same here, possibly still elsewhere.
>  > > > Is this only x86_64 compile tested?
>  > > 
>  > > Of course, who still has 32bit only hardware anyway ;-)
>  > > 
>  > > Will fix, thanks for spotting that.
>  > 
>  > Hrmm, on that, does it really make sense to maintain the i386 code path?
>  > 
>  > How frequently is that code called and what i386 only chips support
>  > aperf/mperf, atom?
> 
> any 64-bit cpu that supports it can have a 32bit kernel installed on it.
> (and a significant number of users actually do this).

1) we really should be pushing those people to run 64bit kernels

[ I'm still hoping distros will start shipping 64bit kernels and have
  the bootloader pick the 64bit one when the hardware supports lm ]

2) those cpus aren't real bad at 64bit divisions :-)

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