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Subject: RE: [RFC][PATCH] i386 x86-64 Eliminate Local APIC timer interrupt
Date: Sat, 30 Apr 2005 14:40:18 -0500
Message-ID: <19D0D50E9B1D0A40A9F0323DBFA04ACCE04B3C@USRV-EXCH4.na.uis.unisys.com>
Thread-Topic: [RFC][PATCH] i386 x86-64 Eliminate Local APIC timer interrupt
Thread-Index: AcVNIhaYl6CXroAzQxa3TZpQchPclQAiFOBw
From: "Protasevich, Natalie" <Natalie.Protasevich@UNISYS.com>
To: "Zwane Mwaikambo" <zwane@arm.linux.org.uk>,
       "Venkatesh Pallipadi" <venkatesh.pallipadi@intel.com>
Cc: "Andrew Morton" <akpm@osdl.org>, "Linus Torvalds" <torvalds@osdl.org>,
       <mingo@elte.hu>, "linux-kernel" <linux-kernel@vger.kernel.org>,
       "Rajesh Shah" <rajesh.shah@intel.com>,
       "John Stultz" <johnstul@us.ibm.com>, "Andi Kleen" <ak@suse.de>,
       "Asit K Mallick" <asit.k.mallick@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1710
Lines: 40

> On Fri, 29 Apr 2005, Venkatesh Pallipadi wrote:
> 
> > Proposed Fix: 
> > Attached is a prototype patch, that tries to eliminate the 
> dependency 
> > on local APIC timer for update_process_times(). The patch 
> gets rid of 
> > Local APIC timer altogether. We use the timer interrupt (IRQ 0) 
> > configured in broadcast mode in IOAPIC instead (Doesn't 
> work with 8259).
> > As changing anything related to basic timer interrupt is a 
> little bit 
> > risky, I have a boot parameter currently ("useapictimer") to switch 
> > back to original local APIC timer way of doing things.
> 
> I'm rather reluctant to advocate the broadcast scheme as i 
> can see it breaking on a lot of systems, e.g. SMP systems 
> which use i8259 (as you noted), IBM x440 and ES7000. If 
> anything the default mode should be APIC timer and have a 
> parameter to disable it. Regarding things like variable timer 
> ticks, reprogramming the PIT is slow, and using it 
> extensively for such sounds like a step in the wrong 
> direction. Is this feature/bug going to proliferate amongst 
> newer processor local APICs?
> 
> Thanks,
> 	Zwane

I did preliminary testing of the patch applied to the rc3 on the IA-32
ES7000, and it booted fine, without the useapictimer boot option. As
Zwane pointed out correctly, ES7000 doesn't handle IRQ broadcast. The
kernel by-passed the non-apic timer option (chose pin1 in check_timer)
and came up safely with local APIC timer.
Thanks,
--Natalie
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