Messages in this thread | | | Date | Wed, 22 Mar 2006 13:39:43 -0500 | From | "Bill Rugolsky Jr." <> | Subject | Re: libata/sata_nv latency on NVIDIA CK804 [was Re: AMD64 X2 lost ticks on PM timer] |
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On Wed, Mar 22, 2006 at 05:09:08PM +0100, Andi Kleen wrote: > perfctr0 is already programmed. You can just use rdpmc on it > > Also my latest patchkit has a debugging patch for lost tries > > ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/lost-cli-debug
Excellent.
> Can you test it with this patch?
I'll give it a try this evening; the test box is an FC5 upgrade guinea pig at the moment, and only half-migrated.
> I'm still not quite convinced you're barking at the right tree > with these latency traces because it doesn't match the symptoms.
Yes, I agree that that the latency issue is not due to the inb(), as I get lost ticks almost continuously at 1 KHZ, and the inb()-related latency occurs with much lower frequency.
However, a 17ms inb() latency is rather dismal, and I need to address that hardware issue, perhaps by purchasing a 4-port card.
I have not been chasing the other issue because the test box appears to keep perfect time with the -rt patch (on SMP) and NTP doesn't complain at all; I haven't yet had the chance to determine whether that is entirely due to John Stultz's new code, or if the preemption is responsible.
-Bill
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