From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id D1A5ADDE2D for ; Sat, 4 Aug 2007 12:28:20 +1000 (EST) Subject: Re: [patch 06/10] 40x decrementer fixes From: Benjamin Herrenschmidt To: Sergei Shtylyov In-Reply-To: <46B35C07.4090806@ru.mvista.com> References: <20070803160900.069522000@linux.vnet.ibm.com> > <20070803161710.931656000@linux.vnet.ibm.com> > <46B35C07.4090806@ru.mvista.com> Content-Type: text/plain Date: Sat, 04 Aug 2007 12:28:11 +1000 Message-Id: <1186194491.5733.2.camel@gruick> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org, paulus@samba.org Reply-To: benh@kernel.crashing.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, 2007-08-03 at 20:47 +0400, Sergei Shtylyov wrote: > Josh Boyer wrote: > > > Allow generic_calibrate_decr to work for 40x platforms. Given that the hardware > > behavior is identical, this also changes the set_dec function to reload the PIT > > on 40x to match the behavior 44x currently has. > > Why bother doing this?! This will only warrant you imprecise decrementer > interrupts while it should be interrupting at the precise period currently (if > you load PIT once)... Because that's what the kernel timekeeping code expects ? The reference time is the timebase and it doesn't drift. The DEC/PIT is commonly used to trigger any timing, such as what is done for lost interrupts on some platforms. Also, with dynticks, we'll most certainly want variable reload values as well. So I'm very happy to have Josh change the code that way. It makes things more consistent accross the board and removes confusion. Ben.