From: Brian Woods <brian.woods@amd.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
Brian Woods <brian.woods@amd.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH] x86: use VMLOAD for PV context switch
Date: Thu, 16 Aug 2018 17:04:09 -0500 [thread overview]
Message-ID: <20180816220408.GC9630@amd.com> (raw)
In-Reply-To: <5B4486F302000078001D290A@prv1-mh.provo.novell.com>
On Tue, Jul 10, 2018 at 04:14:11AM -0600, Jan Beulich wrote:
> Having noticed that VMLOAD alone is about as fast as a single of the
> involved WRMSRs, I thought it might be a reasonable idea to also use it
> for PV. Measurements, however, have shown that an actual improvement can
> be achieved only with an early prefetch of the VMCB (thanks to Andrew
> for suggesting to try this), which I have to admit I can't really
> explain. This way on my Fam15 box context switch takes over 100 clocks
> less on average (the measured values are heavily varying in all cases,
> though).
>
> This is intentionally not using a new hvm_funcs hook: For one, this is
> all about PV, and something similar can hardly be done for VMX.
> Furthermore the indirect to direct call patching that is meant to be
> applied to most hvm_funcs hooks would be ugly to make work with
> functions having more than 6 parameters.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
I have confirmed it with a senior hardware engineer and using vmload in
this fashion is safe and recommended for performance. As far as using
vmload with PV.
Acked-by: Brian Woods <brian.woods@amd.com>
--
Brian Woods
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next prev parent reply other threads:[~2018-08-16 22:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-10 10:14 [PATCH] x86: use VMLOAD for PV context switch Jan Beulich
2018-08-16 22:04 ` Brian Woods [this message]
2018-08-17 7:33 ` Jan Beulich
2018-08-17 14:55 ` Brian Woods
2018-08-17 15:58 ` Jan Beulich
2018-08-29 7:06 ` Ping: " Jan Beulich
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