Messages in this thread | | | Date | Fri, 1 May 2015 18:34:32 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry |
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* Rik van Riel <riel@redhat.com> wrote:
> > I can understand people running hard-RT workloads not wanting to > > see the overhead of a timer tick or a scheduler tick with variable > > (and occasionally heavy) work done in IRQ context, but the jitter > > caused by a single trivial IPI with constant work should be very, > > very low and constant. > > Not if the realtime workload is running inside a KVM guest.
I don't buy this:
> At that point an IPI, either on the host or in the guest, involves a > full VMEXIT & VMENTER cycle.
So a full VMEXIT/VMENTER costs how much, 2000 cycles? That's around 1 usec on recent hardware, and I bet it will get better with time.
I'm not aware of any hard-RT workload that cannot take 1 usec latencies.
Thanks,
Ingo
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