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Tao Zhao wrote:
>
> Hi, all
>
> I want to measure the overhead of LVS, e.g. the additional latency imposed
> by LVS instead of a traditional router. I looked up several documents
> and found Zhang's paper mentioned 60us for rewriting a 536 bytes packet.
> All measurements in other documents focuses on throughput instead of
> latency overhead.
This point seems to be missed by most people. I tried to measure the latency
http://www.linuxvirtualserver.org/Joseph.Mack/performance/single_realserver_performance.html
see section 2.1
but found the difference between latency when using the director to
forward packets as a router and using the director to foward packets
as an LVS director, was too small to measure. My resolution was <100usec
but I couldn't measure it accurately.
> I believe it's not very hard to measure the latency as long as we have a
> fine grain clock. Anyone knows how to get fine grain time?
The attached routine measures the current time with a resolution of usec.
You take the time before and after and subtract the two numbers.
Joe
--
Joseph Mack PhD, Senior Systems Engineer, Lockheed Martin
contractor to the National Environmental Supercomputer Center,
mailto:mack.joseph@xxxxxxx ph# 919-541-0007, RTP, NC, USA /*When is from hint.c */
/* "HINT" -- Hierarchical INTegration. */
/* Copyright (C) 1994 by Iowa State University Research Foundation, Inc. */
#include <time.h>
#include <sys/time.h>
double when()
{
double now;
struct timeval tp;
gettimeofday(&tp, NULL);
//now = ((double) tp.tv_sec + ((double) tp.tv_usec) * 1e-6);
//printf ("when: now %f \n", now);
//printf ("when: tv_sec %d tv_usec %d \n", tp.tv_sec, tp.tv_usec);
return ((double) tp.tv_sec + ((double) tp.tv_usec) * 1e-6);
}
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