From owner-freebsd-hackers  Fri Dec  4 07:20:51 1998
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Received: (from majordom@localhost)
          by hub.freebsd.org (8.8.8/8.8.8) id HAA11114
          for freebsd-hackers-outgoing; Fri, 4 Dec 1998 07:20:51 -0800 (PST)
          (envelope-from owner-freebsd-hackers@FreeBSD.ORG)
Received: from labinfo.iet.unipi.it (labinfo.iet.unipi.it [131.114.9.5])
          by hub.freebsd.org (8.8.8/8.8.8) with SMTP id HAA11094
          for <hackers@FreeBSD.ORG>; Fri, 4 Dec 1998 07:20:44 -0800 (PST)
          (envelope-from luigi@labinfo.iet.unipi.it)
Received: from localhost (luigi@localhost) by labinfo.iet.unipi.it (8.6.5/8.6.5) id OAA08387; Fri, 4 Dec 1998 14:08:30 +0100
From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Message-Id: <199812041308.OAA08387@labinfo.iet.unipi.it>
Subject: Re: Nonblocking page fetching
To: toasty@home.dragondata.com (Kevin Day)
Date: Fri, 4 Dec 1998 14:08:30 +0100 (MET)
Cc: hackers@FreeBSD.ORG
In-Reply-To: <199812041504.JAA04986@home.dragondata.com> from "Kevin Day" at Dec 4, 98 09:04:19 am
X-Mailer: ELM [version 2.4 PL23]
Content-Type: text
Sender: owner-freebsd-hackers@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

> > > This has some obvious disadvantages, but it stopped my movie player from
> > > sitting in vmwait when it could be doing other things.
> > 
> > is it so bad ? The forked process should consume very little memory
...
> Well, I may be wrong, but I assumed that the CPU involved in just having a
> kernel bring pages in on it's own would be less. Is there anything that
> could be saved by putting this in the kernel?

let's see... you fork a process once so that does not count. Every
bunch of prefetch requires an IPC, and every page causes a context
switch (or two ?) following the page fault. This is what you can save.
I cannot quantify times for all the above activities, maybe someone
else has some numbers.

>>> One final note... Does anyone know what effect turning off the bzero on new
>>> pages would be? Security is not an issue in this system, as it's not

i think a lot of software will break.

>> again how bad is it ? bzero is generally done in the idle loop if i am
...
> We are at 100% cpu constantly. When I'm not drawing, i'm prerendering frames

ok, so think this differently: bzero'ing occurs at memory speed which
could be around 200-400MB/s in your case, or 10-20us/page.

	luigi


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message