CODEWITHSUNDEEP
iphoneiosipadprofilingcortex-a8
Ted Middleton
Ted Middleton

Reputation: 7304

Low level cycle counter in iOS devices

Now that it's clear that the Cortex-A8 performance counters aren't available on the iPhone/iPad (they need to be explicitly enabled for usermode, which Apple hasn't done), is there some other way of getting a reasonable cycle count on iOS devices, for micro-profiling?

Upvotes: 4

Views: 941

Answers (2)

zoul
zoul

Reputation: 104095

I might be completely off, but is CFAbsoluteTimeGetCurrent too coarse for you?

Upvotes: 1

hotpaw2
hotpaw2

Reputation: 70733

The most fine grain timing available to iOS user code via a public API appears to be using mach_absolute_time(), from mach/mach_time.h, whose output appears to scaled results from one of the ASIC's clock cycle counters. Call it one extra time just before you start timing to pre-fill the ICACHE with the mach_time library code. Note that some of Apple's ASICs may shift gears for the app's CPU core clock speed, depending.

Upvotes: 3

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