How to measure performance inside Kernel?

[graeme.russ@gmail.com (Graeme Russ)]

Hi Peter,

On 02/11/2012 11:22 AM, Peter Senna Tschudin wrote:
> Jeff,
>
> Thanks for the fast reply. My goal is to determine if the code:
>
> /* * */
> buf_ptr_end = q->bufs[q->num_buffers];
>
> for (buf_ptr = q->bufs[0]; buf_ptr < buf_ptr_end; ++buf_ptr)
> 	buf_ptr->state = VB2_BUF_STATE_DEQUEUED;
> /* * */
>
> is faster than:
>
> /* * */
> for (i = 0; i < q->num_buffers; ++i)
> 	q->bufs[i]->state = VB2_BUF_STATE_DEQUEUED;
> /* * */

For starters, I would not be surprised if the compiler produces identical
code, and if not, code that has the same performance...

> I'm measuring the running time of that portion of code 512 times. Then
> calculate the geometrical mean of results. See one output example:
>
> Original_code:,
>
514,110,92,104,107,101,101,99,105,99,87,105,99,105,105,102,108,123,105,113,104,128,107,92,117,117,120,102,105,105,90,105,101,119,119,101,141,111,96,99,93,80,102,78,93,93,108,108,129,105,107,113,104,104,93,95,104,125,104,95,90,108,117,126,93,87,102,99,93,108,96,104,113,89,92,134,107,98,95,104,102,143,102,126,99,111,99,117,105,102,108,108,98,107,104,98,96,81,108,120,102,87,93,93,93,119,104,96,108,93,108,108,111,98,98,116,122,98,101,87,99,99,105,102,108,111,99,96,111,111,102,98,110,125,107,110,132,102,99,105,87,84,108,120,90,101,95,113,101,107,111,105,108,114,126,102,92,110,104,101,99,108,135,105,123,111,108,102,102,110,110,92,98,104,119,102,113,95,107,104,116,131,153,164,152,125,107,101,93,105,96,123,96,111,111,99,93,101,92,107,89,95,108,111,99,111,114,108,99,117,129,107,105,87,87,93,102,99,83,96,84,102,96,90,110,101,116,89,98,119,125,114,99,126,123,102,123,111,102,101,110,107,111,90,105,111,96,105,102,113,104,158,101,87,102,96,108,111,138,102,120,87,90,102,104,107,101,84,102,99,96,111,
99,105,102,99,104,131,116,104,104,105,126,105,116,128,107,101,105,120,132,111,90,90,114,99,86,110,95,81,120,96,126,99,108,114,120,102,120,125,95,104,96,108,105,105,114,123,111,93,104,83,113,107,99,99,99,105,90,78,119,113,98,98,90,99,90,129,96,101,110,77,110,125,101,102,87,87,117,126,117,108,126,108,96,108,99,105,105,114,123,104,104,110,105,84,96,105,96,120,111,120,101,110,110,87,105,114,102,87,108,135,117,132,141,105,113,95,98,84,96,87,98,89,108,105,102,99,99,105,126,99,101,92,98,75,102,102,129,102,99,102,99,108,92,110,125,107,110,102,96,96,117,72,108,123,105,120,120,99,120,98,104,89,102,117,129,123,105,119,107,101,87,117,111,99,108,117,114,114,90,122,113,95,104,125,113,102,108,120,90,108,93,89,86,87,90,84,83,108,99,102,90,108,90,108,87,95,86,90,123,135,93,126,93,102,99,123,108,117,105,102,105,98,107,122,119,125,96,108,131,99,114,104,93,96,95,83,99,84,92,87,
>
> The geometrical mean of the values is: 104.7623578604
>
> Isn't it enough?

That sounds like a perfectly good methodology - It would be interesting to
see how many reps are required before the mean settles down to a constant
value - Maybe you don't need to run it so many times, or maybe you need to
 run more...

Regards,

Graeme