Re: [RFC][PATCH] srcu: Implement call_srcu()
From: Marcelo Tosatti
Date: Wed Feb 01 2012 - 08:54:23 EST
On Wed, Feb 01, 2012 at 01:01:38PM +0200, Avi Kivity wrote:
> 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
> > 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.
get dirty log: 5634134 ns for 262144 dirty pages
5ms (for the entire operation).
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