Message-ID: <55A5FA2E.1040406@linux.vnet.ibm.com>
Date: Wed, 15 Jul 2015 11:44:06 +0530
From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Organization: IBM
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To: Waiman Long <Waiman.Long@hp.com>
CC: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        Scott J Norton <scott.norton@hp.com>,
        Douglas Hatch <doug.hatch@hp.com>, Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH v2 5/6] locking/pvqspinlock: Opportunistically defer kicking
 to unlock time
References: <1436926417-20256-1-git-send-email-Waiman.Long@hp.com> <1436926417-20256-6-git-send-email-Waiman.Long@hp.com>
In-Reply-To: <1436926417-20256-6-git-send-email-Waiman.Long@hp.com>
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On 07/15/2015 07:43 AM, Waiman Long wrote:
> Performing CPU kicking at lock time can be a bit faster if there
> is no kick-ahead. On the other hand, deferring it to unlock time is
> preferrable when kick-ahead can be performed or when the VM guest is
> having too few vCPUs that a vCPU may be kicked twice before getting
> the lock. This patch implements the deferring kicking when either
> one of the above 2 conditions is true.
>
> Linux kernel builds were run in KVM guest on an 8-socket, 4
> cores/socket Westmere-EX system and a 4-socket, 8 cores/socket
> Haswell-EX system. Both systems are configured to have 32 physical
> CPUs. The kernel build times before and after the patch were:
>
> 		    Westmere			Haswell
>    Patch		32 vCPUs    48 vCPUs	32 vCPUs    48 vCPUs
>    -----		--------    --------    --------    --------
>    Before patch   3m27.4s    10m32.0s	 2m00.8s    14m52.5s
>    After patch	 3m01.3s     9m50.9s	 2m00.5s    13m28.1s
>
> On Westmere, both 32/48 vCPUs case showed some sizeable increase
> in performance. For Haswell, there was some improvement in the
> overcommitted (48 vCPUs) case.
>
> Signed-off-by: Waiman Long <Waiman.Long@hp.com>
> ---

Hi Waiman,

For virtual guests, from my experiments, lock waiter preemption was the
main concern especially with fair locks.
I find that these set of patches are in right direction to address them.

Thanks for the patches.

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