Re: [RFC][PATCH] srcu: Implement call_srcu()

[Avi Kivity <avi@redhat.com>]

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