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From: Paolo Bonzini <pbonzini@redhat.com>
To: Yunhong Jiang <yunhong.jiang@linux.intel.com>, kvm@vger.kernel.org
Cc: mtosatti@redhat.com, rkrcmar@redhat.com, kernellwp@gmail.com,
	David Matlack <dmatlack@google.com>
Subject: Re: [RFC PATCH V3 0/5] Utilizing VMX preemption for timer virtualization
Date: Mon, 6 Jun 2016 14:45:37 +0200	[thread overview]
Message-ID: <d78adeda-9929-31fa-9baa-8316f1f3e4e4@redhat.com> (raw)
In-Reply-To: <1465000951-13343-1-git-send-email-yunhong.jiang@linux.intel.com>



On 04/06/2016 02:42, Yunhong Jiang wrote:
> It adds a little bit latency for each VM-entry because we need setup the
> preemption timer each time.

Really it doesn't according to your tests:

> 1. enable_hv_timer=Y.
> 
> 000004 002174
> 000005 042961
> 000006 479383
> 000007 071123
> 000008 003720
> 
> 2. enable_hv_timer=N.
> 
> # Histogram
> ......
> 000005 000042
> 000006 000772
> 000007 008262
> 000008 200759
> 000009 381126
> 000010 008056

So perhaps you can replace that paragraph with "The benefits offset the
small extra work to do on each VM-entry to setup the preemption timer".

I'll play with this patch and kvm-unit-tests in the next few days.

David, it would be great if you could also try this on your
message-passing benchmarks (e.g. TCP_RR).  On one hand they are heavy on
vmexits, on the other hand they also have many expensive TSC deadline
WRMSRs.  I have requested a few small changes, but I am very happy with
the logic and the vmentry cost.

Thanks,

Paolo

  parent reply	other threads:[~2016-06-06 12:45 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-04  0:42 [RFC PATCH V3 0/5] Utilizing VMX preemption for timer virtualization Yunhong Jiang
2016-06-04  0:42 ` [RFC PATCH V3 1/5] Rename the vmx_pre/post_block to pi_pre/post_block Yunhong Jiang
2016-06-04  0:42 ` [RFC PATCH V3 2/5] Add function for left shift and 64 bit division Yunhong Jiang
2016-06-06 12:37   ` Paolo Bonzini
2016-06-04  0:42 ` [RFC PATCH V3 3/5] Utilize the vmx preemption timer Yunhong Jiang
2016-06-06 12:37   ` Paolo Bonzini
2016-06-04  0:42 ` [RFC PATCH V3 4/5] Separate the start_sw_tscdeadline Yunhong Jiang
2016-06-04  0:42 ` [RFC PATCH V3 5/5] Utilize the vmx preemption timer for tsc deadline timer Yunhong Jiang
2016-06-06 12:36   ` Paolo Bonzini
2016-06-06 12:45 ` Paolo Bonzini [this message]
2016-06-06 18:26   ` [RFC PATCH V3 0/5] Utilizing VMX preemption for timer virtualization yunhong jiang
2016-06-07 16:31   ` David Matlack
2016-06-07 19:30   ` David Matlack
2016-06-08  4:18 ` Wanpeng Li
2016-06-13 20:56   ` yunhong jiang

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