How to measure performance inside Kernel?

[Peter Senna Tschudin]

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;
/* * */

The second code is found at at line 1195 of
drivers/media/video/videobuf2-core.c. I'm doing the tests to see if it
does justify to make a patch or not.

> If you didn't disable interrupts before executing the above, the timing
> of the above loop would include any time spent servicing interrupts.
> Likewise if there were context switches or soft IRQs running. All would
> inflate the perceived time to execute your loop.

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?

Thanks! :-)

-- 
Peter Senna Tschudin
peter.senna at gmail.com
gpg id: 48274C36