On Tue, 2012-04-24 at 14:50 +0200, Jean Pihet wrote: > Hi Tero, > > On Tue, Apr 24, 2012 at 2:21 PM, Tero Kristo <t-kristo@xxxxxx> wrote: > > On Tue, 2012-04-24 at 16:08 +0530, Santosh Shilimkar wrote: > >> + Tero > >> > >> On Tuesday 24 April 2012 03:20 PM, Jean Pihet wrote: > >> > Hi Grazvydas, Kevin, > >> > > >> > I did some gather some performance measurements and statistics using > >> > custom tracepoints in __omap3_enter_idle. > >> > All the details are at > >> > http://www.omappedia.org/wiki/Power_Management_Device_Latencies_Measurement#C1_performance_problem:_analysis > >> > . > >> > > >> Nice data. > >> > >> > The setup is: > >> > - Beagleboard (OMAP3530) at 500MHz, > >> > - l-o master kernel + functional power states + per-device PM QoS. It > >> > has been checked that the changes from l-o master do not have an > >> > impact on the performance. > >> > - The data transfer is performed using dd from a file in JFFS2 to > >> > /dev/null: 'dd if=/tmp/mnt/a of=/dev/null bs=1M count=32'. > > > > Question: what is used for gathering the latency values? > I used ftrace tracepoints which are supposed to be low overhead. I > checked that the overhead cannot be measured on the measurement > interval (>400us), given the fact that the time base is 31us (32 KHz > clock). If you want to get accurate measurements, you could use ARM performance counters, namely the cycle counter. I have a couple of patches for that purpose I've used if you are interested. -Tero -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
