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xen-devel
Re: [Xen-devel] vgettimeofday disabled?
On 3/9/08 16:48, "Chris Lalancette" <clalance@xxxxxxxxxx> wrote:
> Hello,
> Based on a comment from a customer, I looked briefly at the vgettimeofday
> implementation in Xen. I noticed that vgettimeofday is disabled in the 64-bit
> linux-2.6.18-xen.hg tree, basically by setting sysctl_vsyscall = 0 in
> vsyscall_init(). Is there some known problem with enabling this? In a quick
> test, I turned it on, and went from 2m14s in my micro benchmark to 30s for the
> benchmark, but I'm not sure if there will be any ill effects from the same.
We probably don't update vxtime structure, so you likely get dodgy results
from do_vgettimedofday(). However, forcing vxtime to track vcpu0's time info
obtained from Xen would probably be quite easy to do and may be accurate
enough.
But, without that extra engineering, I recommend you check what answers
you're getting from gettimeofday(). Could be quite a significant
performance/correctness tradeoff ;-)
-- Keir
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