From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Mosberger Date: Tue, 23 Sep 2003 14:59:11 +0000 Subject: Re: NS83820 2.6.0-test5 driver seems unstable on IA64 Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org >>>>> On Tue, 23 Sep 2003 03:51:18 -0700, "David S. Miller" said: David> On Tue, 23 Sep 2003 20:40:05 +1000 Peter Chubb David> wrote: >> How expensive is it to take the trap and do a fix up, compared to >> making an aligned copy? As it involves raising and handling a >> fault disassembling the instruction that caused the fault, etc., >> I'd be surprised if it's much less than 1000 cycles, even without >> the printk, although I haven't measured it yet, and can't find >> enough info in the architecture manuals to know what it is. David> A cache miss can cause 100 or so cycles. :) David> And unlike the fixup trap, the printk wakes up a process and David> causes disk activity as syslogd writes to the kernel message David> log file. The printk() is rate-controlled and doesn't happen for every unaligned access. It's average cost can be made as low as we want to, by adjusting the rate. --david