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Re: [Qemu-devel] [PATCH v7 1/5] cpu: Provide vcpu throttling interface
From: |
Juan Quintela |
Subject: |
Re: [Qemu-devel] [PATCH v7 1/5] cpu: Provide vcpu throttling interface |
Date: |
Wed, 09 Sep 2015 13:01:03 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
Paolo Bonzini <address@hidden> wrote:
> On 09/09/2015 12:41, Juan Quintela wrote:
>>> > + qemu_mutex_unlock_iothread();
>>> > + atomic_set(&cpu->throttle_thread_scheduled, 0);
>>> > + g_usleep(sleeptime_ns / 1000); /* Convert ns to us for usleep call */
>>> > + qemu_mutex_lock_iothread();
>>
>> Why is this thread safe?
>>
>> qemu_mutex_lock_iothread() is protecting (at least) cpu_work_first on
>> each cpu. How can we be sure that _nothing_ will change that while we
>> are waiting?
>
> You only have to be sure that the queued work list remains consistent;
> not that nothing changes.
But nothing else is protected by the iothread? That is the part that I
can't see.
> (BTW, there is a queued patch that moves the queued work list to its own
> mutex, and indeed it releases that mutex while calling the work function).
>> A fast look through the tree don't show anything that
>> runs here that drops the lock.
>
> Actually, the existing implementation of throttling does. :)
See, that happens when you search in a modified tree O:-)
Thanks for the fast answer.
Later, Juan.
- [Qemu-devel] [PATCH v7 2/5] migration: Parameters for auto-converge cpu throttling, (continued)
[Qemu-devel] [PATCH v7 3/5] migration: Dynamic cpu throttling for auto-converge, Jason J. Herne, 2015/09/08
Re: [Qemu-devel] [PATCH v7 0/5] migration: Dynamic cpu throttling for auto-converge, Juan Quintela, 2015/09/09