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Re: [Xen-devel] Question about hyper-threading of domains

To: Jacob Gorm Hansen <jacobg@xxxxxxx>
Subject: Re: [Xen-devel] Question about hyper-threading of domains
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 29 Apr 2005 20:59:26 +0100
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On 29 Apr 2005, at 20:42, Jacob Gorm Hansen wrote:

is it possible, and will it make sense, to allow an SMP-domain access to both SMT/Hyper threads of a CPU?

My performance measurements of the small address spaces implementation (SAS) seem to indicate that having the driver domain in a separate hyper thread is still a little faster than SAS for a non-SMP/SMT domU. I guess that means that that SMT IPIs are about the same cost as ring switches.

HT is designed to look almost identical to SMP, so it is no problem to give both HTs to a multi-processor domain. This will make sense if the domain is running a workload that benefits from HT (e.g., probably certain types of multi-threaded application).

In most cases I expect it will give better overall performance to allocate the second HT solely to a driver domain.

 -- Keir

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