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Re: [Qemu-devel] [PULL 11/24] tcg: enable thread-per-vCPU

From: Laurent Vivier
Subject: Re: [Qemu-devel] [PULL 11/24] tcg: enable thread-per-vCPU
Date: Mon, 27 Feb 2017 13:48:48 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

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    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.


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