Messages in this thread | | | Date | Tue, 10 Jun 2014 20:45:34 +0300 | From | Stratos Karafotis <> | Subject | Re: [PATCH 3/7] cpufreq: intel_pstate: Add debugfs file stats |
| |
On 10/06/2014 08:05 μμ, Dirk Brandewie wrote: > On 06/10/2014 09:21 AM, Stratos Karafotis wrote: >> On 10/06/2014 06:47 μμ, Dirk Brandewie wrote: >>> On 06/09/2014 02:00 PM, Stratos Karafotis wrote: >>>> Add stats file in debugfs under driver's parent directory >>>> (pstate_snb) which counts the time in nsecs per requested >>>> P state and the number of times the specific state >>>> was requested. >>>> >>>> The file presents the statistics per logical CPU in the >>>> following format. The time is displayed in msecs: >>>> >>> >>> NAK >>> >>> This adds significantly to the memory footprint to gather information >>> that is available by post processing the perf tracepoint information. >>> The increase isn't horrible on single socket desktop processor machines >>> but gets big with server class machines. One vendor I have talked to considers >>> a machine with 1024 cpus to be a SMALL machine. >>> >> >> If I am not wrong the sizeof pstate_stat is 20B. On my CPU with 20 P states, we >> need 400B per logical CPU (3200B total in my desktop) plus 64B for stats pointers. >> >> In your example this would need about 400KB - 500KB? >> Is it too much for 1024 a CPUs system? > > For something that will likely not be used IMO yes. > >> >> I think it's a useful piece of info that we can have it directly without >> post processing tracepoint. >> Is it acceptable to conditionally compile it with a new CONFIG option? > > > I can see where the information could be useful but the set of people > that would find it useful is very small. Having information about residency > since boot is interesting but just barely. This file will encourage people > to build tools/scripts that rely on this file and they will complain bitterly > if/when it changes or goes away so you would be creating a defacto ABI in > debugfs. > > > This functionality will *not* be supportable in up coming processors where HWP > is being used. See section 14.4 of the current SDM vol. 3 > http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-system-programming-manual-325384.pdf >
I will drop this patch in v2. Thanks a lot for your comments and your time!
Stratos
-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |