From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailserv2.iuinc.com (qmailr@mailserv2.iuinc.com [206.245.164.55]) by sod.res.cmu.edu (8.8.7/8.8.7) with SMTP id MAA22775 for ; Thu, 25 Mar 1999 12:20:11 -0500 Received: from milano.cup.hp.com (root@milano.cup.hp.com [15.13.185.124]) by palrel1.hp.com (8.8.6/8.8.5tis) with ESMTP id JAA17501 for ; Thu, 25 Mar 1999 09:19:59 -0800 (PST) Received: from localhost (grundler@localhost [127.0.0.1]) by milano.cup.hp.com with SMTP (8.8.6 (PHNE_14041)/8.7.3 TIS Messaging 5.0) id JAA18711 for ; Thu, 25 Mar 1999 09:18:52 -0800 (PST) Message-Id: <199903251718.JAA18711@milano.cup.hp.com> To: hppa-linux@thepuffingroup.com Subject: Re: [hppa-linux] Qn on PA-RISC Page tables and TLB In-reply-to: Your message of "Wed, 24 Mar 1999 23:10:36 PST." Date: Thu, 25 Mar 1999 09:18:51 -0800 From: Grant Grundler List-ID: Kumar wrote: ... > Other interesting point to note is that PA-RISC does not > define how many entries in the table etc. Very much unlike > x86. The CPU pdir can vary in size. For a HW walker, it must be allocated in physically configuous memory, this pretty much fixes the size once it's setup. The size of the CPU PDIR is determined mostly by memory size, amount of I/O space required (Legacy PA requires memory mapped I/O), and some fudge factor. Sizing it to allow a HW walker find all physical mappings is good for performance. I assume this also helps SW TLB handlers by reducing hash collisions. However, I'm not the expert on CPU pdir. K, C-class, and T600 also have an I/O pdir. This is only useful for systems with more than 4GB (3.75GB?) of physical memory since PA (and current PCI devices) can only use 32-bits of addressing. The I/O pdir size depends on how much I/O one wants to allow mapped at any given time and it too must be physically contigous. 16/th to 8th of physical memory seems to be a pretty good rule of thumb. For now, I would say ignore the I/O pdir until hppa-linux has a login prompt. If the OS doesn't use the I/O pdir, it just implies the DMA is not coherent with Processor activity - just like on an x86 box. I haven't studied Linux I/O subsytem enough to know where/how to integrate support for an I/O pdir. I hope the HP-UX docs released help explain this - search for keyword "CDIO". grant