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Re: [Qemu-devel] [PULL 11/24] tcg: enable thread-per-vCPU
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [PULL 11/24] tcg: enable thread-per-vCPU |
Date: |
Mon, 27 Feb 2017 14:38:21 +0000 |
User-agent: |
mu4e 0.9.19; emacs 25.2.7 |
Laurent Vivier <address@hidden> writes:
> Le 24/02/2017 à 12:20, Alex Bennée a écrit :
>> There are a couple of changes that occur at the same time here:
>>
>> - introduce a single vCPU qemu_tcg_cpu_thread_fn
>>
>> One of these is spawned per vCPU with its own Thread and Condition
>> variables. qemu_tcg_rr_cpu_thread_fn is the new name for the old
>> single threaded function.
>>
>> - the TLS current_cpu variable is now live for the lifetime of MTTCG
>> vCPU threads. This is for future work where async jobs need to know
>> the vCPU context they are operating in.
>>
>> The user to switch on multi-thread behaviour and spawn a thread
>> per-vCPU. For a simple test kvm-unit-test like:
>>
>> ./arm/run ./arm/locking-test.flat -smp 4 -accel tcg,thread=multi
>>
>> Will now use 4 vCPU threads and have an expected FAIL (instead of the
>> unexpected PASS) as the default mode of the test has no protection when
>> incrementing a shared variable.
>>
>> We enable the parallel_cpus flag to ensure we generate correct barrier
>> and atomic code if supported by the front and backends. This doesn't
>> automatically enable MTTCG until default_mttcg_enabled() is updated to
>> check the configuration is supported.
>
> This commit breaks linux-user mode:
>
> debian-8 with qemu-ppc on x86_64 with ltp-full-20170116
>
> cd /opt/ltp
> ./runltp -p -l "qemu-$(date +%FT%T).log" -f /opt/ltp/runtest/syscalls -s
> setgroups03
>
> setgroups03 1 TPASS : setgroups(65537) fails, Size is >
> sysconf(_SC_NGROUPS_MAX), errno=22
> qemu-ppc: /home/laurent/Projects/qemu/include/qemu/rcu.h:89:
> rcu_read_unlock: Assertion `p_rcu_reader->depth != 0' failed.
> qemu-ppc: /home/laurent/Projects/qemu/include/qemu/rcu.h:89:
> rcu_read_unlock: Assertion `p_rcu_reader->depth != 0' failed.
> qemu-ppc: /home/laurent/Projects/qemu/include/qemu/rcu.h:89:
> rcu_read_unlock: Assertion `p_rcu_reader->depth != 0' failed.
> ...
Interesting. I can only think the current_cpu change has broken it
because most of the changes in this commit affect softmmu targets only
(linux-user has its own run loop).
Thanks for the report - I'll look into it.
--
Alex Bennée
- [Qemu-devel] [PULL 02/24] mttcg: translate-all: Enable locking debug in a debug build, (continued)
- [Qemu-devel] [PULL 02/24] mttcg: translate-all: Enable locking debug in a debug build, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 03/24] mttcg: Add missing tb_lock/unlock() in cpu_exec_step(), Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 04/24] tcg: move TCG_MO/BAR types into own file, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 06/24] tcg: add kick timer for single-threaded vCPU emulation, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 01/24] docs: new design document multi-thread-tcg.txt, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 05/24] tcg: add options for enabling MTTCG, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 07/24] tcg: rename tcg_current_cpu to tcg_current_rr_cpu, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 10/24] tcg: enable tb_lock() for SoftMMU, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 11/24] tcg: enable thread-per-vCPU, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 08/24] tcg: drop global lock during TCG code execution, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 09/24] tcg: remove global exit_request, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 12/24] tcg: handle EXCP_ATOMIC exception for system emulation, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 14/24] cputlb: tweak qemu_ram_addr_from_host_nofail reporting, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 13/24] cputlb: add assert_cpu_is_self checks, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 15/24] cputlb: introduce tlb_flush_* async work., Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 17/24] cputlb: add tlb_flush_by_mmuidx async routines, Alex Bennée, 2017/02/24
- [Qemu-devel] [PULL 22/24] target-arm: ensure all cross vCPUs TLB flushes complete, Alex Bennée, 2017/02/24