On Mon, Jan 31, 2000 at 11:57:47PM +0000, John Storrs wrote:
>
> Victor
>
> Is there a description somewhere of what the RT-Linux kernel does during the
> execution of an RTL task with incoming interrupts destined for Linux. If not,
> could you or Michael please provide one? Do you just acknowledge, record, and
> return to the RTL task, or do you execute some top halves. What about Counter
> 0 - do you lose jiffies, or is this handled specially? In a performance test
Ack, record, and return. In non-io-apic x86s, putting in the rtl_timer module
adds code that takes irq 0 for rtl, reads the clock and reprogram
and keep track of time.
> which reads the TSC sequentially inside an RTL task, I'm seeing significant
> maximum jitter (17us with an ISA network card; 3us with a PCI network card
> under same network loading) which must be interrupt related.
It's the revolting ISA bus. 3us is pretty good for pci, better than I measure.
But the difference is the 12-15us an ISA bus transaction: these can lock the
entire system. I have measured
read tsc
write 1 byte to isa bus
read tsc
and can get 12us if the system is busy.
> --
> John Storrs, Laboratory for Micro Enterprise
> 125 Culham 1 Site, Culham, Abingdon OX14 3DA, UK
> tel/fax 01865 407085 email [EMAIL PROTECTED]
> www http://www.i-way.co.uk/~storrs
>
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