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From: Keir Fraser <keir.xen@gmail.com>
To: Dan Magenheimer <dan.magenheimer@oracle.com>,
	Jan Beulich <JBeulich@novell.com>
Cc: xen-devel@lists.xensource.com,
	"winston.l.wang" <winston.l.wang@intel.com>
Subject: Re: [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits
Date: Fri, 15 Apr 2011 18:28:09 +0100	[thread overview]
Message-ID: <C9CE3EB9.16691%keir.xen@gmail.com> (raw)
In-Reply-To: <e1e889c5-4d60-4162-a7d2-04423d8bbea9@default>

On 15/04/2011 15:34, "Dan Magenheimer" <dan.magenheimer@oracle.com> 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

  reply	other threads:[~2011-04-15 17:28 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-04-14  7:18 [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits Jan Beulich
2011-04-14  7:25 ` Keir Fraser
2011-04-14  7:42   ` Jan Beulich
2011-04-14  7:50     ` Keir Fraser
2011-04-14  8:06       ` Jan Beulich
2011-04-14  9:18         ` Keir Fraser
2011-04-14 22:41           ` Dan Magenheimer
2011-04-15  6:40             ` Keir Fraser
2011-04-15 14:34               ` Dan Magenheimer
2011-04-15 17:28                 ` Keir Fraser [this message]
2011-04-14  7:28 ` Jan Beulich
2011-04-14 16:05 ` Keir Fraser
2011-04-14 16:28   ` Jan Beulich
2011-04-14 16:48     ` Keir Fraser
2011-04-14 18:33       ` Wang, Winston L
2011-04-14 21:06         ` Keir Fraser
2011-04-14 21:37           ` Wang, Winston L
2011-04-15  7:06           ` Jan Beulich
2011-04-15  7:08       ` Jan Beulich
2011-04-15  7:37         ` Keir Fraser
2011-04-15 14:49           ` Wang, Winston L

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