netdev - Re: rps perfomance WAS(Re: rps: question

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Message-ID: <1271590476.16881.4925.camel@edumazet-laptop>
Date:	Sun, 18 Apr 2010 13:34:36 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	hadi@...erus.ca
Cc:	Changli Gao <xiaosuo@...il.com>, Rick Jones <rick.jones2@...com>,
	David Miller <davem@...emloft.net>, therbert@...gle.com,
	netdev@...r.kernel.org, robert@...julf.net, andi@...stfloor.org
Subject: Re: rps perfomance WAS(Re: rps: question

Le dimanche 18 avril 2010 à 11:39 +0200, Eric Dumazet a écrit :
> No, only one packet per IPI, since I setup my tg3 coalescing parameter
> to the minimum value, I received one packet per interrupt.
> 
> The specific app is :
> 
> for f in `seq 1 8`; do while :; do :; done& done
> 

An other interesting user land app would be to use a cpu _and_ memory
cruncher, because of caches misses we'll get.

$ cat nloop.c
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define SZ 4*1024*1024

int main(int argc, char *argv[])
{
	int nproc = 8;
	char *buffer;

	if (argc > 1)
		nproc = atoi(argv[1]);
	while (nproc > 1) {
		if (fork() == 0)
			break;
		nproc--;
	}
	buffer = malloc(SZ);
	while (1)
		memset(buffer, 0x55, SZ);
}

$ ./nloop 8 &

echo 00 >/sys/class/net/eth3/queues/rx-0/rps_cpus
4861ms

echo 01 >/sys/class/net/eth3/queues/rx-0/rps_cpus
4981ms

echo 02 >/sys/class/net/eth3/queues/rx-0/rps_cpus
7191ms

echo 04 >/sys/class/net/eth3/queues/rx-0/rps_cpus
7128ms

echo 08 >/sys/class/net/eth3/queues/rx-0/rps_cpus
7107ms

echo 10 >/sys/class/net/eth3/queues/rx-0/rps_cpus
5505ms

echo 20 >/sys/class/net/eth3/queues/rx-0/rps_cpus
7125ms

echo 40 >/sys/class/net/eth3/queues/rx-0/rps_cpus
7022ms

echo 80 >/sys/class/net/eth3/queues/rx-0/rps_cpus
7157ms


Maximum overhead is 7191-4861 = 23.3 us per packet



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