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Re: [Qemu-devel] [PATCH 12/18] Insert event_tap_mmio() to cpu_physical_m


From: Yoshiaki Tamura
Subject: Re: [Qemu-devel] [PATCH 12/18] Insert event_tap_mmio() to cpu_physical_memory_rw() in exec.c.
Date: Wed, 27 Apr 2011 23:19:41 +0900

On Apr 27, 2011, at 2:51 PM, Takuya Yoshikawa <address@hidden> wrote:

> 
>>>> What kind of mmio should be traced here, device or CPU originated? Or both?
>>>> 
>>>> Jan
>>>> 
>>>> 
>>> 
>>> To let Kemari replay outputs upon failover, tracing CPU originated
>>> mmio (specifically write requests) should be enough.
>>> IIUC, we can reproduce device originated mmio as a result of cpu
>>> originated mmio.
>>> 
> 
> Sorry, but I don't understand why it is safe yet.
> 
> The problem is not if the mmio's are to be replayed but if replaying
> them will produce the same result, is it?

No.  That's the functionality of event-tap queuing.
The mmio tap is for recording which CPU originated mmio resulted in I/O 
monitored at event-tap queuing.

We expect the replayed result to be same as the primary, but we don't have to 
guarantee while it's queued.

Thanks,

Yoshi

> 
> In other words, is it really idempotent?
> 
> Takuya
> 
>> 
>> OK, I see.
>> 
>> But this tap will only work for KVM. I think you either have to catch
>> the other paths that TCG could take as well or maybe better move the
>> hook into kvm-all - then it's absolutely clear that this is no generic
>> feature.
>> 
>> Jan
>> 




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