Re: [Xen-devel] [Patch 2 of 2]: PV-domain SMP performance Linux-part

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 19.12.08 10:10 >>>
>I haven't seen any win on any real world setup. So I remain unconvinced, and
>it'll need more than you alone championing the patch to get it in. There
>have been no other general comments so far (Jan's have been about specific
>details).

I think I'd generally welcome a change like this, but I'm not certain how far
I feel convinced that the submission meets one very basic criteria:
avoidance of mis-use of the feature by a domain (simply stating that a vCPU
will be de-scheduled after 1ms anyway doesn't seem sufficient to me). This
might need to include ways to differentiate between Dom0/DomU and/or
CPU- vs IO-bound vCPU-s.

Beyond that, it seems questionable that tying this to event delivery being
disabled on the vCPU is very useful - Xen could do this on its own, without
needing a second flag. Having an extra flag really seems useful only when
one can set it while holding spin locks, which at least the Linux part of the
patch doesn't seem to aim at.

Jan


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