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Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs u
| To: | Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx> |
|---|---|
| Subject: | Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits |
| From: | Keir Fraser <keir.xen@xxxxxxxxx> |
| Date: | Fri, 15 Apr 2011 18:28:09 +0100 |
| Cc: | xen-devel@xxxxxxxxxxxxxxxxxxx, "winston.l.wang" <winston.l.wang@xxxxxxxxx> |
| Delivery-date: | Fri, 15 Apr 2011 10:28:44 -0700 |
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| Thread-topic: | [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits |
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On 15/04/2011 15:34, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote: >>> Agreed. In fact, maybe it should be asserted in write_tsc? >> >> We still write_tsc on CPU physical hot-add. > > Hmmm... IIRC the testing that Intel was doing for hot-add was > not for processors that were actually electrically hot-plugged > but only for processors that were powered-on at the same > time as all other processors but left offline until needed > (e.g. for capacity-on-demand). For this situation, writing > to tsc is still the wrong approach. I don't think we finished > the discussion about electrically hot-plugged processors > because they didn't exist... don't know if they do yet either. > IIRC I had proposed an unnamed boot parameter that said > "this machine may add unsynchronized processors post-boot" > and disallow hot-add processors if not specified (or if > not specified AND a run-time check of a hot-add processor > shows non-synchronization). Well, I think the case I'm thinking of is electrical hot-plug. Not sure. Either way I doubt anyone is actually using the feature. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel |
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