timing in driver function
I have a function in a driver which takes ~50ms to execute, which I've measured by reading jiffies at the beginning and end. But jiffies only counts at 128Hz on my system, so this was a very coarse measurement. Now I would like to find out more exactly where the time is going inside this function. So my basic question is, what is the best way to measure lapsed time with reasonable resolution on an OMAP?
As I had done with the jiffies measurement, what I imagined was inserting lines into my function, sampling the value of some counter at various points within it. This approach is crude but simple and would suffice for my case.
Since it must be a very common task, I thought I'd ask here what the recommended approach is. I see a few directions...
1. Using the OMAP's 32kHz timer, which is provided as a "struct clocksource". It seems like what I would want is to call clocksource_32k.read(), but I don't know how to retrieve clocksource_32k.
2. Using the ARM core's Performance Monitor Count Registers. This seems to be what perf_event uses. I'm not familiar with perf_events, but it sounds like I would also need to build 'perf', which according to
http://www.omappedia.org/wiki/Using_perf isn't possible to cross-compile. I don't want to tackle that without some reassurance that it is the right/only way.
I am currently using a 2.6.38 kernel.
thanks,
Michael
MATRIX VISION GmbH, Talstrasse 16, DE-71570 Oppenweiler
Registergericht: Amtsgericht Stuttgart, HRB 271090
Geschaeftsfuehrer: Gerhard Thullner, Werner Armingeon, Uwe Furtner, Erhard Meier
Quoted 12 lines · Michael Jones
I have a function in a driver which takes ~50ms to execute, which I've measured by reading jiffies at the beginning and end. But jiffies only counts at 128Hz on my system, so this was a very coarse measurement. Now I would like to find out more exactly where the time is going inside this function. So my basic question is, what is the best way to measure lapsed time with reasonable resolution on an OMAP?
As I had done with the jiffies measurement, what I imagined was inserting lines into my function, sampling the value of some counter at various points within it. This approach is crude but simple and would suffice for my case.
Quoted 7 lines
Since it must be a very common task, I thought I'd ask here what the recommended approach is. I see a few directions...
1. Using the OMAP's 32kHz timer, which is provided as a "struct clocksource". It seems like what I would want is to call
clocksource_32k.read(), but I don't know how to retrieveclocksource_32k.
If you're looking for a one-off profiling, then as a hack, you could export a function that unconditionally returns the value of the 32kHz timer's count register (32KSYNCNT_CR) and use that for profiling.
- Anand
Quoted 16 lines · Anand
Quoted 15 lines · Michael Jones
I have a function in a driver which takes ~50ms to execute, which I've measured by reading jiffies at the beginning and end. But jiffies only counts at 128Hz on my system, so this was a very coarse measurement. Now I would like to find out more exactly where the time is going inside this function. So my basic question is, what is the best way to measure lapsed time with reasonable resolution on an OMAP?
As I had done with the jiffies measurement, what I imagined was inserting lines into my function, sampling the value of some counter at various points within it. This approach is crude but simple and would suffice for my case.
Since it must be a very common task, I thought I'd ask here what the recommended approach is. I see a few directions...
Quoted 9 lines
Quoted 4 lines
1. Using the OMAP's 32kHz timer, which is provided as a "struct clocksource". It seems like what I would want is to call
clocksource_32k.read(), but I don't know how to retrieveclocksource_32k.If you're looking for a one-off profiling, then as a hack, you could export a function that unconditionally returns the value of the 32kHz timer's count register (32KSYNCNT_CR) and use that for profiling.
How about using GPT using dm-timer APIs?
Quoted 6 lines
- Anand
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Hi,
Quoted 12 lines · Michael Jones
I have a function in a driver which takes ~50ms to execute, which I've measured by reading jiffies at the beginning and end. But jiffies only counts at 128Hz on my system, so this was a very coarse measurement. Now I would like to find out more exactly where the time is going inside this function. So my basic question is, what is the best way to measure lapsed time with reasonable resolution on an OMAP?
As I had done with the jiffies measurement, what I imagined was inserting lines into my function, sampling the value of some counter at various points within it. This approach is crude but simple and would suffice for my case.
Quoted 6 lines
Since it must be a very common task, I thought I'd ask here what the recommended approach is. I see a few directions...
1. Using the OMAP's 32kHz timer, which is provided as a "struct clocksource". It seems like what I would want is to call
clocksource_32k.read(), but I don't know how to retrieveclocksource_32k.
Consider getnstimeofday(). It's not OMAP-specific; there are several examples in the Linux codebase[1]; and if you use a higher-resolution clocksource, the resolution should also increase (try disabling CONFIG_OMAP_32K_TIMER).
- Paul
Hi Paul,
Quoted 30 lines · Paul Walmsley
Hi,
Quoted 12 lines · Michael Jones
I have a function in a driver which takes ~50ms to execute, which I've measured by reading jiffies at the beginning and end. But jiffies only counts at 128Hz on my system, so this was a very coarse measurement. Now I would like to find out more exactly where the time is going inside this function. So my basic question is, what is the best way to measure lapsed time with reasonable resolution on an OMAP?
As I had done with the jiffies measurement, what I imagined was inserting lines into my function, sampling the value of some counter at various points within it. This approach is crude but simple and would suffice for my case.
Quoted 6 lines
Since it must be a very common task, I thought I'd ask here what the recommended approach is. I see a few directions...
1. Using the OMAP's 32kHz timer, which is provided as a "struct clocksource". It seems like what I would want is to call
clocksource_32k.read(), but I don't know how to retrieveclocksource_32k.Consider
getnstimeofday(). It's not OMAP-specific; there are several examples in the Linux codebase[1]; and if you use a higher-resolution clocksource, the resolution should also increase (try disablingCONFIG_OMAP_32K_TIMER).
Quoted 4 lines
- Paul
Thanks, I took your suggestion and it served my purpose just fine.
-Michael
MATRIX VISION GmbH, Talstrasse 16, DE-71570 Oppenweiler
Registergericht: Amtsgericht Stuttgart, HRB 271090
Geschaeftsfuehrer: Gerhard Thullner, Werner Armingeon, Uwe Furtner, Erhard Meier