Date: Sun, 12 Mar 2000 12:16:22 -0800 (PST) From: aron@cs.rice.edu To: freebsd-gnats-submit@FreeBSD.org Subject: i386/17346: APIC cannot be enabled without turning on support for SMP Message-ID: <200003122016.MAA35704@freefall.freebsd.org>
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>Number: 17346 >Category: i386 >Synopsis: APIC cannot be enabled without turning on support for SMP >Confidential: no >Severity: serious >Priority: medium >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: sw-bug >Submitter-Id: current-users >Arrival-Date: Sun Mar 12 12:20:01 PST 2000 >Closed-Date: >Last-Modified: >Originator: Mohit Aron >Release: FreeBSD-current >Organization: Rice University >Environment: FreeBSD aurora.cs.rice.edu 4.0-20000208-CURRENT FreeBSD 4.0-20000208-CURRENT #1: Mon Feb 14 19:59:00 CST 2000 root@vaddr.cs.rice.edu:/usr/src/sys/compile/VADDR i386 >Description: The FreeBSD kernel only supports enabling the APIC when SMP support is configured in the kernel. APICs are desirable even in uniprocessor systems because they provide 1) on chip timers 2) larger number of IRQs and 3) low interrupt overheads. Unfortunately, if the FreeBSD kernel is compiled with SMP support, the performance drops down - possibly due to the various locking mechanisms that get turned on. A webserver's performance drops down by 22% when SMP support is turnedon a an otherwise uniprocessor machine. >How-To-Repeat: Trying compiling the kernel after turning on the option APIC_IO in the kernel configuration file. Make sure that the option SMP is not turned on. Kernel wouldn't compile. >Fix: The FreeBSD kernel should support turning on the APIC without turning on SMP support. This is useful in uniprocessor systems. >Release-Note: >Audit-Trail: >Unformatted: To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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