Messages in this thread | | | Date | Sat, 16 Sep 2006 13:30:35 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108 |
| |
* Jes Sorensen (jes@sgi.com) wrote:
> If you want to prove people wrong, I suggest you do some real life > implementation and measure some real workloads with a predefined set of > tracepoints implemented using kprobes and LTT and show us that the > benchmark of the user application suffers in a way that can actually be > measured. Argueing that a syscall takes an extra 50 instructions > because it's traced using kprobes rather than LTT doesn't mean it > actually has any real impact. >
And about those extra cycles.. according to : Documentation/kprobes.txt "6. Probe Overhead
On a typical CPU in use in 2005, a kprobe hit takes 0.5 to 1.0 microseconds to process. Specifically, a benchmark that hits the same probepoint repeatedly, firing a simple handler each time, reports 1-2 million hits per second, depending on the architecture. A jprobe or return-probe hit typically takes 50-75% longer than a kprobe hit. When you have a return probe set on a function, adding a kprobe at the entry to that function adds essentially no overhead.
i386: Intel Pentium M, 1495 MHz, 2957.31 bogomips k = 0.57 usec; j = 1.00; r = 0.92; kr = 0.99; jr = 1.40
x86_64: AMD Opteron 246, 1994 MHz, 3971.48 bogomips k = 0.49 usec; j = 0.76; r = 0.80; kr = 0.82; jr = 1.07
ppc64: POWER5 (gr), 1656 MHz (SMT disabled, 1 virtual CPU per physical CPU) k = 0.77 usec; j = 1.31; r = 1.26; kr = 1.45; jr = 1.99
So, 1 microsecond seems more like 1500-2000 cycles to me, not 50.
Mathieu
OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |