linux-kernel - Re: [tbench regression fixes]: digging out smelly deadmen.

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Date:	Fri, 31 Oct 2008 12:42:34 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	shemminger@...tta.com, zbr@...emap.net, rjw@...k.pl, mingo@...e.hu,
	s0mbre@...rvice.net.ru, a.p.zijlstra@...llo.nl,
	LKML <linux-kernel@...r.kernel.org>,
	Netdev <netdev@...r.kernel.org>, efault@....de,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [tbench regression fixes]: digging out smelly deadmen.

On Fri, 31 Oct 2008, David Miller wrote:

> From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
> Date: Fri, 31 Oct 2008 11:40:16 +0200 (EET)
> 
> > Let me remind that it is just a single process, so no ping-pong & other 
> > lock related cache effects should play any significant role here, no? (I'm 
> > no expert though :-)).
> 
> Not locks or ping-pongs perhaps, I guess.  So it just sends and
> receives over a socket, implementing both ends of the communication
> in the same process?

Effectively its this:

signal(SIGALRM, alarm_handler);
...
while (flag) { /* flagged by alarm_handler */
	loops = 90
	open & setup sockets & connection
	while (--loops > 0) {
		write(wr_fd, buf, size);
		read(rd_fd, buf, size);
	}
	close sockets
}

where size comes from this array (advancing in the inner loop one by one):

static int sizes[] = {
        1, 3, 5, 7, 16, 32, 64, 512, 1024, 2048,        /* misc. sizes */
        1, 3, 5, 7, 16, 32, 64, 512, 1024, 2048,
        32, 32, 32, 32, 32, 32,         /* x windows mostly... */
        512, 512, 512, 512, 512,        /* DBMS's mostly */
};

buf sits in the stack and is not initialized (besides reading into it).

...I think the rest is just bogus complexity :-) ...maybe I should just 
take that from above as basis for Reduced AIM9 benchmark, it nearly 
compiles already.

> If hash chain conflicts do happen for those 2 sockets, just traversing
> the chain 2 entries deep could show up.

No idea on this one.


-- 
 i.