linux-kernel - Re: [RFC][PATCH] srcu: Implement call

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Message-ID: <4F291E1F.3030505@oss.ntt.co.jp>
Date:	Wed, 01 Feb 2012 20:12:31 +0900
From:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
To:	Avi Kivity <avi@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>, paulmck@...ux.vnet.ibm.com,
	Oleg Nesterov <oleg@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [RFC][PATCH] srcu: Implement call_srcu()

(2012/02/01 20:01), Avi Kivity wrote:
> On 02/01/2012 01:00 PM, Takuya Yoshikawa wrote:

>> How about just doing:
>>
>> take a spin_lock
>> copy the entire (or some portions of) bitmap locally
>> clear the bitmap
>> unlock
>>
>
> That means that vcpus dirtying memory also have to take that lock, and
> spin while the bitmap is being copied.  So kvm_vm_ioctl_get_dirty_log()
> will become faster, at the expense of vcpus, which I think is a bad
> tradeoff.

Almost every caller is already holding the mmu_lock.

Isn't it possible to make others hold the lock only for the case of
marking to the bitmap? (I will check myself too.)


>> write protect the dirty pages based on the copied dirty data
>>
>> copy_to_user
>>
>>
>>
>> I can show you some performance numbers, this weekend, if you like.
>
> That'll be great, numbers are better than speculation.
>

Yes, I already have some good numbers to show (and some patches).

	Takuya
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