Re: NS83820 2.6.0-test5 driver seems unstable on IA64

David Mosberger
2003-09-23T14:59:11Z

>>>>> 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