From owner-freebsd-hackers  Tue Jul 15 01:25:15 1997
Return-Path: <owner-hackers>
Received: (from root@localhost)
          by hub.freebsd.org (8.8.5/8.8.5) id BAA14770
          for hackers-outgoing; Tue, 15 Jul 1997 01:25:15 -0700 (PDT)
Received: from labinfo.iet.unipi.it (labinfo.iet.unipi.it [131.114.9.5])
          by hub.freebsd.org (8.8.5/8.8.5) with SMTP id BAA14722;
          Tue, 15 Jul 1997 01:24:00 -0700 (PDT)
Received: from localhost (luigi@localhost) by labinfo.iet.unipi.it (8.6.5/8.6.5) id JAA12495; Tue, 15 Jul 1997 09:19:25 +0200
From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Message-Id: <199707150719.JAA12495@labinfo.iet.unipi.it>
Subject: Re: interrupt latency
To: Shimon@i-Connect.Net (Simon Shapiro)
Date: Tue, 15 Jul 1997 09:19:25 +0200 (MET DST)
Cc: smp@csn.net, hackers@FreeBSD.ORG, smp@FreeBSD.ORG
In-Reply-To: <XFMail.970715010210.Shimon@i-Connect.Net> from "Simon Shapiro" at Jul 15, 97 01:01:51 am
X-Mailer: ELM [version 2.4 PL23]
Content-Type: text
Sender: owner-hackers@FreeBSD.ORG
X-Loop: FreeBSD.org
Precedence: bulk

> I have microtime calls in the DPT driver.  If I understand it correctly, on
> a P6-200 I could have 200 times better resolution with access to the
> registers in the CPU.  I see interrupt latency of 0-3us with UP, and about

perhaps 200 is too much (since any cpu stall, cache miss, etc. will hit
you with a fair number of wasted cycles) but certainly 10-20 times
better resolution.

	Luigi