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Re: [Qemu-devel] [big lock] Discussion about the convention of device's
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock |
Date: |
Thu, 20 Sep 2012 10:27:17 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120828 Thunderbird/15.0 |
Il 20/09/2012 10:09, liu ping fan ha scritto:
> >
> > No, MMIO dispatch has to discard the fine-grained lock before acquiring
> > the big lock.
>
> This will cause the device state broken, and expose device under changing
> risk.
We do it all the time with asynchronous I/O.
It's just an invariant that fine-grain-locked devices have to obey. You
cannot keep the same semantics you enjoyed when a single lock covered
everything.
> > If you allow
> >
> > lock(fine)
> > lock(coarse)
> >
> > then the (presumably higher-priority) thread that is requesting the
> > fine-grained lock must wait for the lower-priority thread that holds the
> > coarse-grained lock. Then you get priority inversion.
>
> Which thread has higher-priority? Why does the thread with coarse lock
> have lower-priority?
Because there can be so many things happening under the coarse lock,
that just _assuming_ it has lower priority is a good thing.
On the other hand, if the device didn't need immediate servicing (which
means higher priority), you wouldn't bother taking it out of the big
QEMU lock.
Paolo
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, (continued)
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Avi Kivity, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, liu ping fan, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Paolo Bonzini, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, liu ping fan, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Avi Kivity, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Jan Kiszka, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Jan Kiszka, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, liu ping fan, 2012/09/20
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Paolo Bonzini, 2012/09/20
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, liu ping fan, 2012/09/20
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock,
Paolo Bonzini <=
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Avi Kivity, 2012/09/20
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, liu ping fan, 2012/09/21
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Paolo Bonzini, 2012/09/21
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Avi Kivity, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Paolo Bonzini, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Avi Kivity, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Paolo Bonzini, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Avi Kivity, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Jan Kiszka, 2012/09/19
- Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock, Avi Kivity, 2012/09/19