Subject: Re: PS/2 mouse latency was Re: [linux-audio-dev] Re: [DATAPOINT] kernels and latencies
From: Richard Gooch (rgooch_AT_ras.ucalgary.ca)
Date: Tue Jul 04 2000 - 21:04:59 EEST
Andi Kleen writes:
> On Mon, Jul 03, 2000 at 10:18:30PM -0600, Richard Gooch wrote:
> > Andrew Morton writes:
> > > Roger Larsson wrote:
> > > > Note: I have seen X causing 50 ms latencies...
> > > > [aux_write_dev+26/28]
> > >
> > > awwwww.. Yuk. What a piggy little function!
> >
> > Yuck! It's even disabling interrupts for that long.
>
> Does anybody know if it just stupid locking or if the hardware
> requires interrupts off ?
Someone who understands the PC KBD controller should answer that. It
looks like command/read/ack cycles should not be interspersed with
other KBD accesses. That would not be an unreasonable hardware
limitation.
So with all that locking, the ISR may have to wait a long time for the
lock to yield. Even if other interrupts are not blocked, this will
still delay BH/tasklet processing, not to mention scheduling
latencies.
Someone more familiar with the current IRQ subsystem could help here:
- what happens if the interrupt handler does nothing with the
keyboard: does the interrupt keep banging the CPU and hence the
handler keeps getting run
- can we block delivery of an interrupt, so that other interrupts and
process rescheduling continues as normal?
Regards,
Richard....
Permanent: rgooch_AT_atnf.csiro.au
Current: rgooch_AT_ras.ucalgary.ca
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