Date: Sun, 22 Nov 2015 13:50:31 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Mark Johnston <markj@FreeBSD.org> Cc: freebsd-arch@FreeBSD.org Subject: Re: zero-cost SDT probes Message-ID: <20151122105031.GP48728@zxy.spb.ru> In-Reply-To: <20151122024542.GA44664@wkstn-mjohnston.west.isilon.com> References: <20151122024542.GA44664@wkstn-mjohnston.west.isilon.com>
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On Sat, Nov 21, 2015 at 06:45:42PM -0800, Mark Johnston wrote:
> Hi,
>
> For the past while I've been experimenting with various ways to
> implement "zero-cost" SDT DTrace probes. Basically, at the moment an SDT
> probe site expands to this:
>
> if (func_ptr != NULL)
> func_ptr(<probe args>);
>
> When the probe is enabled, func_ptr is set to dtrace_probe(); otherwise
> it's NULL. With zero-cost probes, the SDT_PROBE macros expand to
>
> func(<probe args>);
I am experimenting with overhead DTrace probes in userspace.
Total executing time program w/o any probes 3% less then program with
not enabled probes.
With enabled probes (conditional probes too) -- each probe add about 0.7us.
I am place DTrace probe inside inner loop, worst case.
=====
#include <stdio.h>
#include "probes.h"
long primes[1000000] = { 3 };
long primecount = 1;
int main(int argc, char **argv)
{
long divisor = 0;
long currentprime = 5;
long isprime = 1;
while (currentprime < 1000000)
{
isprime = 1;
PRIMES_PRIMECALC_START(currentprime);
for(divisor=0;divisor<primecount;divisor++)
{
PRIMES_PRIMECALC_ITER(divisor);
if (currentprime % primes[divisor] == 0)
{
isprime = 0;
break;
}
}
PRIMES_PRIMECALC_DONE(currentprime,isprime);
if (isprime)
{
primes[primecount++] = currentprime;
PRIMES_PRIMECALC_TABLESIZE(primecount);
// printf("%d is a prime\n",currentprime);
}
currentprime = currentprime + 2;
}
printf("Total %ld primes\n", primecount);
}
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