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

[Avi Kivity]

On 02/01/2012 01:00 PM, Takuya Yoshikawa wrote:
>
>> rcu_assign_pointer), and use atomic operations to copy and clear:
>>
>>    word = bitmap[i]
>>    put_user(word)
>>    atomic_and(&bitmap[i], ~word)
>>
>>
>
> This kind of this was really slow IIRC.
>
>
> 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.

> 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.

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/