[ECOS] Regarding timing measurements for eCos

Abhi abhi@4961ocean.org
Thu Dec 9 21:04:00 GMT 2004


Hi,
I am doing some performance benchmarks for ecos on iPAQ.
eCos version 2+ from the cvs repository
Last Changelog entry is
{
   2003-03-27  Bart Veer  <bartv@ecoscentric.com>

        * configure.in, configure:
        Look for the host-side sources in tools/src as well as in host, as
        per the 2.0 release tree.
        Look for per-package host-side software in any/all versions of a
        package, not just "current".
}

I ran the tm_basic.cxx test case to obtain some numbers for simple tests:

Platform: Compaq iPAQ Pocket PC (StrongARM 1110)
Copyright (C) 2000, 2001, Red Hat, Inc.
                                 Confidence
     Ave     Min     Max     Var  Ave  Min  Function
  ======  ======  ======  ====== ========== ========
...
    1.64    1.63    2.98    0.03   97%  97% Thread switch

I guess Thread switch takes about 1.64 micro-seconds.

I modified the tcp_lo_test.c to measure the performance of tcp loopback 
communication

In the server() I added
        if ((len = read(e_source, data_buf, MAX_BUF)) < 0  )
        {
            CYG_TEST_FAIL_FINISH( "I/O error" );
        }
        HAL_CLOCK_READ(&tcp_test[test_iter].end); // get the raw clock 
ticks after reading the data
        cyg_semaphore_post(&wait_for_server);


While in the client ()

    wait_for_tick();
    for (test_iter = 0; test_iter < nsamples; ++test_iter)
    {
//      diag_printf("Sending %d times\n", i);
//      start_tick = cyg_current_time();
        HAL_CLOCK_READ(&tcp_test[test_iter].start);
        if ((len = write(s_source,data_buf_write,40)) < 0)
        {
            CYG_TEST_FAIL_FINISH( "Error writing buffer");
        }
        cyg_semaphore_wait(&wait_for_server);
    }

    and eventually I called
        show_times_hdr();
    show_times_detail(tcp_test, nsamples, "tcp_one_way_test", true);

 The result shows an average latency of 9975 micro-seconds. This figure 
makes me suspicious. It is too close to 10 ms (the kernel tick time).

Other Questions:
================
1. I guess using HAL_CLOCK_READ for recording an interval is useless if the 
interval is more than 10ms. Is this right?

2. I believe cyg_current_time() on iPAQ has a granularity of 10ms
and HAL_CLOCK_READ returns a number between 0 -- 36864. Thus the 
granularity using HAL_CLOCK_READ is 10ms/36864. Is this correct?

3. If the interval I am trying to measure is more than 10ms, but I want a 
granularity of say 1 micro-second. How do I do that? Do I need to create a 
real_time clock using the get_clock() methods?

thanks
- Abhi




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