From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [203.10.76.45]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mx.ozlabs.org", Issuer "CA Cert Signing Authority" (verified OK)) by bilbo.ozlabs.org (Postfix) with ESMTPS id 4E73DB6EDE for ; Tue, 11 Aug 2009 06:45:58 +1000 (EST) Received: from mail.southpole.se (mail.southpole.se [193.12.106.18]) by ozlabs.org (Postfix) with ESMTP id DF269DDD01 for ; Tue, 11 Aug 2009 06:45:57 +1000 (EST) Subject: Re: 5121 cache handling. From: Kenneth Johansson To: Scott Wood In-Reply-To: <4A808268.6000107@freescale.com> References: <1249649632.4940.38.camel@localhost> <20090807195600.GB11681@b07421-ec1.am.freescale.net> <1249935384.7077.35.camel@localhost> <4A808268.6000107@freescale.com> Content-Type: text/plain Date: Mon, 10 Aug 2009 22:45:53 +0200 Message-Id: <1249937153.7077.38.camel@localhost> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2009-08-10 at 15:26 -0500, Scott Wood wrote: > Kenneth Johansson wrote: > >>> should not the framebuffer be marked as cache write through. that is the > >>> W bit should be set in the tlb mapping. Why is this not done ? is that > >>> feature also not working on 5121 ?? > >> It probably would have been too slow. > > > > how much slower would write through be ? I thought it was not that big > > of a difference from copy back. > > It's a big difference if you're writing out an entire cache line of data > anyway, but because of write-through it goes out one word at a time > without bursting. > > -Scott > Yes the memory system would obviously get a higher load but do the CPU actually see that? do it stall on the write ?