linux-kernel - Re: [PATCH V2 0/2] measure SMI cost (user)

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Message-ID: <20170602182748.GA31764@kernel.org>
Date:   Fri, 2 Jun 2017 15:27:48 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>, elliott@....com,
        Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH V2 0/2] measure SMI cost (user)

Em Fri, Jun 02, 2017 at 03:45:11PM +0000, Liang, Kan escreveu:
> > > On Mon, May 29, 2017 at 02:52:39PM +0200, Peter Zijlstra wrote:
> > > > On Mon, May 29, 2017 at 02:46:37PM +0200, Jiri Olsa wrote:
> > > > > for some reason I can't get single SMI count generated, is there a
> > > > > setup/bench that would provoke that?

> > > > Not having SMIs is a good thing ;-)
> > > > Not sure we can tickle them in a reliable way.

> > > yea I saw some counts last time, now just zero so I was wondering
> > > if it's working

> > We have internal test case which can generate SMI, but I cannot publish the
> > test case. Sorry about that.
 
> APM_CNT (0xB2) could be used to trigger SMI#.

Here if I run the following 'perf stat' command and press the mute
button (the one sharing F1 in a thinkpad t450s it triggers SMIs, toggle
it in quick sucession and it generates more, etc:

[root@...et ~]# perf stat -I 1000 -e msr/smi/
#           time             counts unit events
     1.000103173                  0      msr/smi/                                                    
     2.000278816                  4      msr/smi/                                                    
     3.000472630                  4      msr/smi/                                                    
     4.000743916                  0      msr/smi/                                                    
     5.001369358                  4      msr/smi/                                                    
     6.001668033                  0      msr/smi/                                                    
     7.001852603                  4      msr/smi/                                                    
     8.002108269                 12      msr/smi/                                                    
     9.002367312                  0      msr/smi/                                                    
^C     9.961897866                  0      msr/smi/                                                    

[root@...et ~]#

- Arnaldo
 
> It's documented in PCH datasheet.
> https://www.intel.com/content/dam/www/public/us/en/
> documents/datasheets/9-series-chipset-pch-datasheet.pdf
> 
> APM_CNT-Advanced Power Management Control Port Register 
> I/O Address: B2h 
> Attribute: R/W 
> Default Value: 00h 
> Size: 8 bits
> Lockable: No 
> Usage: Legacy Only
> Power Well: Core
> Bit Description
> 7:0 Used to pass an APM command between the OS and the SMI handler. 
> Writes to this port not only store data in the APMC register, 
> but also generates an SMI# when the APMC_EN bit is set.
> 
> You can write a byte to port 0xB2 to trigger an SMI#
> 
> Thanks,
> Kan