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Re: [Qemu-devel] global_mutex and multithread.
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] global_mutex and multithread. |
Date: |
Thu, 15 Jan 2015 11:44:43 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 |
On 15/01/2015 11:25, Frederic Konrad wrote:
> Hi everybody,
>
> In case of multithread TCG what is the best way to handle
> qemu_global_mutex?
> We though to have one mutex per vcpu and then synchronize vcpu threads when
> they exit (eg: in tcg_exec_all).
The basic ideas from Jan's patch in
http://article.gmane.org/gmane.comp.emulators.qemu/118807 still apply.
RAM block reordering doesn't exist anymore, having been replaced with
mru_block.
The patch reacquired the lock when entering MMIO or PIO emulation.
That's enough while there is only one VCPU thread.
Once you have >1 VCPU thread you'll need the RCU work that I am slowly
polishing and sending out. That's because one device can change the
memory map, and that will cause a tlb_flush for all CPUs in tcg_commit,
and that's not thread-safe.
And later on, once devices start being converted to run outside the BQL,
that can be changed to use new functions address_space_rw_unlocked /
io_mem_read_unlocked / io_mem_write_unlocked. Something like that is
already visible at https://github.com/bonzini/qemu/commits/rcu (ignore
patches after "kvm: Switch to unlocked MMIO").
Paolo
Re: [Qemu-devel] global_mutex and multithread., Mark Burton, 2015/01/15