Hi,
I could suggest to run 10 times the test in a row ;-) but oprofile clearly relies on a configurable timer and not the scheduler tick itself so there is no reason for this limitation, as this is not a rewrite. For example x86 has a CONFIG_OPROFILE_EVENT_MULTIPLEX feature for which developers added /dev/oprofile/time_slice for tuning so no religion here. Probably inherited from the past where platforms were less powerful.
FYI, oprofile "file operations" are set in arch/arm/oprofile/common.c, leveraging ARM Performance Monitoring Unit. But if oprofile.timer is set, oprofile functions are redefined to leverage generic hrtimer. PMU can lose interrupt when register overflows (ARM errata), current potential work-around is to use several counters for same event so that at least 1 of them catches the info :-( not very reliable => so oprofile.timer = 1 shall be the default.
Regards Fred
Frederic Turgis OMAP Platform Business Unit - OMAP System Engineering - Platform Enablement
Texas Instruments France SA, 821 Avenue Jack Kilby, 06270 Villeneuve Loubet. 036 420 040 R.C.S Antibes. Capital de EUR 753.920
-----Original Message-----
From: Tom Gall [mailto:tom.gall@linaro.org] Sent: Tuesday, August 30, 2011 6:03 PM To: Turgis, Frederic Cc: Clark, Rob; Linaro Dev Subject: Re: 11.07 oprofile on panda busted?
On Tue, Aug 30, 2011 at 10:53 AM, Turgis, Frederic f-turgis@ti.com wrote:
Hi,
As indicated by Siamashka, we are expected to operate at
scheduler tick rate, i.e. 128Hz (drivers/oprofile/timer_int.c). From your test, we have 84 ticks, i.e. 656ms of test.
Is that correct ? I checked that also in our Android kernel
and it was the same.
Makes sense, but it brings me back to my earlier lament, that a user tunable option to up the rate for the purpose of collecting more samples would be quite desirable.
The only impacts we have seen in the past are related to
idle time. For same duration, we had less ticks if more idle time. But Android guys, who used it more than us, never really complained on this or timer granularity. Probably this was more orented to multimedia use cases so 10s of s.
Regards Fred
Frederic Turgis OMAP Platform Business Unit - OMAP System Engineering - Platform Enablement
Texas Instruments France SA, 821 Avenue Jack Kilby, 06270
Villeneuve
Loubet. 036 420 040 R.C.S Antibes. Capital de EUR 753.920
-- Regards, Tom
"We want great men who, when fortune frowns will not be discouraged."
- Colonel Henry Knox
Linaro.org ¦ Open source software for ARM SoCs w) tom.gall att linaro.org w) tom_gall att vnet.ibm.com h) tom_gall att mac.com