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[Qemu-devel] Re: kvm crashes with spice while loading qxl

From: Avi Kivity
Subject: [Qemu-devel] Re: kvm crashes with spice while loading qxl
Date: Sun, 06 Mar 2011 12:38:44 +0200
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On 03/05/2011 06:35 PM, Marcelo Tosatti wrote:
Regarding global mutex, TCG and KVM execution behaviour can become more
similar wrt locking by dropping qemu_global_mutex during generation and
execution of TBs.

How can you do that? During generation, a device can assert the reset line, changing cpu modes, or move the memory map.

During execution, tcg accesses memory a lot. So we'll need to acquire qemu_global_mutex for every memory access, and separate protection for TB.

kvm achieves lockless protection by forcing vcpus off and dropping their page tables while executing natively, and using srcu while emulating. We can do something similar for tcg, but it won't be easy.

Of course for memory or PIO accesses from vcpu context qemu_global_mutex
must be acquired.

Yes, and not just mmio - all memory accesses.

With that in place, it becomes easier to justify further improvements
regarding parallelization, such as using a read-write lock for
l1_phys_map / phys_page_find_alloc.

  21.62%               sh            3d38920b3f  [.] 0x00003d38920b3f
   6.38%               sh  qemu-system-x86_64    [.] phys_page_find_alloc

should be replaced by a memslot list probably

   4.90%               sh  qemu-system-x86_64    [.] tb_find_fast
   4.34%               sh  qemu-system-x86_64    [.] tlb_flush

error compiling committee.c: too many arguments to function

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