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 QAA03722 for ; Mon, 29 Mar 1999 16:27:43 -0500 From: Stan Sieler Message-Id: <199903292127.NAA30341@bart.allegro.com> Subject: Re: [hppa-linux] syscall work To: mickey@openbsd.org Date: Mon, 29 Mar 1999 13:27:01 -0800 (PST) Cc: shaver@netscape.com, hppa-linux@thepuffingroup.com In-Reply-To: <199903261703.MAA19278@lucifier.dial-up.user.akula.net> from "Michael Shalayeff" at Mar 26, 99 12:03:26 pm MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-ID: Re: > let's think what is less efficient: extra mapped page, or > extra indirrect ptr reference? > my point is, why map extra page (and waiste extra page) ? > one page is 128 page dir entries, hehe (; returning to the pd discussion) If you're talking about the gateway page, if you don't actually *allocate* a page, but simply rely on the trap that occurs when you try to jump to it, then there's 0 storage cost for the extra mapped page approach...no TLB entry, no entries in other data structures. The only cost is the additional CPU time in the TLB miss handler to say: if isr.ior = 0xc0000400 (or whatever) then handle system call attempt else handle TLB miss BTW, the extra cost of doing a system call mechanism via a non-mapped gateway page vs. using a GATE instruction is about 5 microseconds on a 32MHz machine. -- Stan Sieler sieler@allegro.com http://www.allegro.com/sieler.html