Re: 2.6.23-mm1 breaks C-state support on Intel T7200 x86_64

[Mark Gross <mgross@linux.intel.com>]

On Thu, Nov 08, 2007 at 10:02:12AM -0800, Andrew Morton wrote:
> > On Thu, 08 Nov 2007 12:19:44 -0500 Valdis.Kletnieks@vt.edu wrote:
> > (Sorry for not reporting this sooner - I haven't been running off battery
> > much in the last 3 weeks, so I didn't notice it till now...)
> > 
> > Dell Latitude D820 laptop, T7200 Core2 Duo CPU, x86_64 kernel.
> > 
> > As reported by 'powertop' on a basically idle machine:
> > 
> > 2.6.23-mm1:
> > 
> > Cn                Avg residency       P-states (frequencies)
> > C0 (cpu running)        (100.0%)        2.00 Ghz     0.8%
> > C1                0.0ms ( 0.0%)         1.67 Ghz     0.0%
> > C2                0.0ms ( 0.0%)         1333 Mhz     0.0%
> > C3                0.0ms ( 0.0%)         1000 Mhz    99.2%
> > 
> > 2.6.23-rc8-mm2:
> > 
> > Cn                Avg residency       P-states (frequencies)
> > C0 (cpu running)        ( 0.3%)         2.00 Ghz     0.0%
> > C1                0.0ms ( 0.0%)         1.67 Ghz     0.0%
> > C2                0.0ms ( 0.0%)         1333 Mhz     0.0%
> > C3               31.5ms (99.7%)         1000 Mhz   100.0%
> > 
> > In addition, the ACPI power estimate reported about 25 watts for 23-mm1,
> > but only 21 watts for -rc8-mm2, a significant regression.
> > 
> > I bisected this down to this set of patches:
> > 
> > pm-qos-infrastructure-and-interface.patch
> > pm-qos-infrastructure-and-interface-fix.patch
> > pm-qos-infrastructure-and-interface-vs-git-acpi.patch
> > pm-qos-infrastructure-and-interface-vs-git-acpi-2.patch
> > latencyc-use-qos-infrastructure.patch
> > 
> > The patch says:
> > 
> >   To register the default pm_qos target for the specific parameter, the
> >   process must open one of /dev/[cpu_dma_latency, network_latency,
> >   network_throughput]
> > 
> >   As long as the device node is held open that process has a registered
> >   requirement on the parameter.  The name of the requirement is
> >   "process_<PID>" derived from the current->pid from within the open system
> >   call.
> > 
> > I shouldn't have to have a process open a /dev/file, write a number, and then
> > stay around forever so the file doesn't close in order to get the same behavior
> > I was getting by default before.  What needs to happen to get this to not
> > be a behavior regression/change?
> > 
> 
> That's a great report, thanks.  Over to you, Mark ;)
> 
> btw, I also have a note here that these patches caused Rafael to see an
> smp_call_function() inside local_irq_save().  Did that get fixed?

Ah, I see the problem.  I think I posted a fix to this.  The problem is
that what's in the mm1 tree has a parameter PM_QOS_IDLE that needed to
be PM_QOS_CPU_DMA_LATENCY. 

I'm not sure what's in the current MM tree at this point so I can't say
its been fixed.  Is there an easy way from me to see what's currently in
MM?  

FWIW I think I fixed this when I fixed up Rafael's issue.  Would you
like me to send out a re-fresh patch against 2.6.23-mm1?

--mgross

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