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Re: [Qemu-discuss] Why do additional cores reduce performance?

From: Paolo Bonzini
Subject: Re: [Qemu-discuss] Why do additional cores reduce performance?
Date: Tue, 16 Dec 2014 17:31:13 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0

On 16/12/2014 17:22, Oleg Ovechko wrote:
>> What is your benchmark?
> I've tried different ways (CrystalDiskMark 3.0.3 x64, ATTO Disk
> Banchmark v2.47) all give same result.

All are run on the AHCI passthrough disk(s), right?

> When everything is enabled in BIOS it is 6:23 on real Windows versus
> 9:03 on virtualized...
> Phil Ehrens has sent me link
> https://lists.gnu.org/archive/html/qemu-discuss/2014-10/msg00036.html
> If I don't misunderstand, it means kvm/qemu simply is not designed for
> multi-threading.

No, it means TCG does not support multithreading.  KVM does, and you are
using it.

> I guess I need to try different hypervisor. 50% performance is too
> high price especially when VT-x and VT-d are meant to make it 0%

It is surprising to me too.


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