Messages in this thread | | | From | David Mosberger <> | Date | Tue, 23 Sep 2003 07:59:11 -0700 | Subject | Re: NS83820 2.6.0-test5 driver seems unstable on IA64 |
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>>>>> On Tue, 23 Sep 2003 03:51:18 -0700, "David S. Miller" <davem@redhat.com> said:
David> On Tue, 23 Sep 2003 20:40:05 +1000 Peter Chubb David> <peter@chubb.wattle.id.au> 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
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