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

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Message-ID: <4F293D14.5030008@redhat.com>
Date:	Wed, 01 Feb 2012 15:24:36 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
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()

On 02/01/2012 01:12 PM, Takuya Yoshikawa wrote:
> (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.

True.  But let's not add more locks.

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

Yes, in walk_addr(), while setting accessed and dirty bits in guest
PTEs, or while emulating instructions and writing to guest memory.

>> That'll be great, numbers are better than speculation.
>>
>
>
> Yes, I already have some good numbers to show (and some patches).

Looking forward.

-- 
error compiling committee.c: too many arguments to function

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