From owner-freebsd-hackers Wed Jul 19 20:19: 4 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from boreas.isi.edu (boreas.isi.edu [128.9.160.161]) by hub.freebsd.org (Postfix) with ESMTP id 6C63037B848 for ; Wed, 19 Jul 2000 20:19:01 -0700 (PDT) (envelope-from larse@ISI.EDU) Received: from isi.edu (hbo.isi.edu [128.9.160.75]) by boreas.isi.edu (8.9.3/8.9.3) with ESMTP id UAA08789 for ; Wed, 19 Jul 2000 20:19:00 -0700 (PDT) Message-ID: <39766FA4.C9C2EE1F@isi.edu> Date: Wed, 19 Jul 2000 20:19:00 -0700 From: Lars Eggert Organization: USC Information Sciences Institute X-Mailer: Mozilla 4.73 [en] (X11; I; FreeBSD 4.1-RC i386) X-Accept-Language: en, de MIME-Version: 1.0 To: hackers@freebsd.org Subject: clearing pages in the idle loop Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Hello, if recently read [Dougan99], which describes optimizations to the memory management system of the PowerPC port of the Linux kernel. One of the mechanisms (Section 9) is pushing the clearing of pages to the idle task, like FreeBSD does. The authors report that on the PPC architecture, it is critical that the data and instruction cache be turned off before zeroing pages in the idle loop. Otherwise, cache pollution as a side-effect of idle-time activity would more than cancel out the gains from the zeroing. Wouldn't this be true on the i386 architecture as well? I have seen no calls in the FreeBSD idle loop that seem to do this. I'm not even sure if the i386 architecture supports turning off caches (but a quick glance at the Pentium references seems to indicate so.) Has anybody experimented with the idea before? Lars [Dougan99] Cort Dougan, Paul Mackerras and Victor Yodaiken. Optimizing the Idle Task and Other MMU Tricks. Proceedings 3rd USENIX Symposium on Operating Systems Design and Implementation (OSDI), February 1999, pp. 229-237. -- Lars Eggert Information Sciences Institute http://www.isi.edu/larse/ University of Southern California To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message