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Re: [Qemu-devel] [PATCH 5/9] exec: protect mru_block with RCU
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From: |
Fam Zheng |
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Subject: |
Re: [Qemu-devel] [PATCH 5/9] exec: protect mru_block with RCU |
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Date: |
Thu, 5 Feb 2015 17:30:55 +0800 |
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User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Thu, 02/05 09:37, Paolo Bonzini wrote:
>
>
> On 05/02/2015 07:23, Fam Zheng wrote:
> >> > @@ -1381,14 +1397,16 @@ static ram_addr_t ram_block_add(RAMBlock
> >> > *new_block, Error **errp)
> >> > QTAILQ_INSERT_TAIL(&ram_list.blocks, new_block, next);
> >> > }
> >> > ram_list.mru_block = NULL;
> >> > + atomic_rcu_set(&ram_list.version, ram_list.version + 1);
> >> >
> >> > - ram_list.version++;
> > Why is this not atomic_inc
>
> Because writes are protected by the ramlist lock. atomic_inc is more
> expensive.
OK!
>
> > (or why is atomic_rcu_set necessary here)?
>
> I probably should move it to patch 9; it is needed to update the list
> before ram_list.version.
>
> If you prefer I can change it to
>
> smp_wmb();
> atomic_set(&ram_list.version, ram_list.version + 1);
>
> ?
>
Yes, this looks more obvious :)
Fam
[Qemu-devel] [PATCH 6/9] cosmetic changes preparing for the following patches, Paolo Bonzini, 2015/02/03
[Qemu-devel] [PATCH 8/9] exec: convert ram_list to QLIST, Paolo Bonzini, 2015/02/03
[Qemu-devel] [PATCH 2/9] exec: make iotlb RCU-friendly, Paolo Bonzini, 2015/02/03