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Re: [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + co
From: |
Scott Tsai |
Subject: |
Re: [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments |
Date: |
Thu, 12 Nov 2009 02:37:26 +0800 |
On Thu, Nov 12, 2009 at 2:09 AM, Michael S. Tsirkin <address@hidden> wrote:
>> I do have a newbie question, when exactly would vrtio have to handle
>> concurrent access from multiple threads?
>> My current reading of the code suggests:
>> 1. when CONFIG_IOTHREAD is true
>> 2. when CONFIG_KVM is true and the guest machine has multiple CPUs
>
> Right. I don't think CONFIG_IOTHREAD can work correctly
> without kvm though: how would atomics be handled?
I naively imagined it to work like this:
When CONFIG_IOTHREAD is true and CONFIG_KVM is false,
all the tcg CPUs run in the tcg_cpu_thread and device emulation code
runs in io_thread,
so if the tcg translators generate suitable memory barrier
instructions when it sees a "lfence", "sfence", "mfence" instruction
while emulating a x86 or "sync" while emulating a MIPS everything
should work but a quick look at target-*/translate.c suggests memory
barrier instructions are treated as nops.
So maybe --enable-io-thread while --disable-kvm should not be allowed
at configure time.
Does anyone actually ship qemu with CONFIG_IOTHREAD enabled?
- [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, (continued)
- [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Paul Brook, 2009/11/11
- [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Michael S. Tsirkin, 2009/11/11
- [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Paul Brook, 2009/11/11
- [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Michael S. Tsirkin, 2009/11/11
- [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Paul Brook, 2009/11/11
- [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Michael S. Tsirkin, 2009/11/11
- Re: [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Paul Brook, 2009/11/11
- Re: [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Scott Tsai, 2009/11/11
- Re: [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Michael S. Tsirkin, 2009/11/11
- Re: [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Michael S. Tsirkin, 2009/11/11
- Re: [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments,
Scott Tsai <=
- Re: [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Michael S. Tsirkin, 2009/11/11
- Re: [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Jamie Lokier, 2009/11/12
- [Qemu-devel] Re: [PATCH] qemu/virtio: make wmb compiler barrier + comments, Michael S. Tsirkin, 2009/11/11