From: Paolo Bonzini <pbonzini@redhat.com>
To: Oleg Ovechko <ovechko.spam@gmail.com>,
qemu-discuss@nongnu.org, kvm@vger.kernel.org
Subject: Re: Why do additional cores reduce performance?
Date: Tue, 16 Dec 2014 10:26:05 +0100 [thread overview]
Message-ID: <548FFAAD.5040601@redhat.com> (raw)
In-Reply-To: <CAGwhzhG7NqVPn9cy+gLTMoWYLzpRhUmLqDdMUx_ceLQd723YLg@mail.gmail.com>
On 16/12/2014 00:40, Oleg Ovechko wrote:
> A. Host Windows, 6 cores (no HT, turbo boost off): 6:23 (+- 10 secs)
> B. Host Windows, 1 CPU core (other are turned off in BIOS): 7:13 (+-10 secs)
> C. Host 1 core, Guest Windows 1 core: 7:15 - same as B, no degradation
> D. Host 6 cores, Guest Windows 1 core: 7:57
> E. Host 6 cores, Guest Windows 4 cores: 8:17
What is your benchmark?
Windows sometimes has scalability problems due to the way it does
timing. Try replacing "-cpu host" with "-no-hpet -cpu
host,hv_time,hv_vapic".
> 3. Also I am unsure about HT. When I specify "cores=2",
I suppose you mean "threads=2".
> is there any
> guaranty that whole core with both HT parts is passed to VM? Or it can be
> mix of two real cores with separate caches?
It will be a mix. Do not specify HT in the guest, unless you have HT in
the host _and_ you are pinning the two threads of each guest core to the
two threads of a host core.
Paolo
next prev parent reply other threads:[~2014-12-16 9:26 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-15 23:40 Why do additional cores reduce performance? Oleg Ovechko
2014-12-16 9:26 ` Paolo Bonzini [this message]
2014-12-16 16:22 ` Oleg Ovechko
2014-12-16 16:31 ` Paolo Bonzini
-- strict thread matches above, loose matches on Subject: below --
2014-12-15 23:33 Oleg Ovechko
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