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Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping t
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads |
Date: |
Fri, 19 Jan 2018 14:33:06 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 |
On 19/01/2018 13:36, Pavel Dovgalyuk wrote:
>> From: Paolo Bonzini [mailto:address@hidden
>> Sent: Friday, January 19, 2018 3:26 PM
>> To: Pavel Dovgalyuk; 'Pavel Dovgalyuk'; address@hidden
>> Cc: address@hidden; address@hidden; address@hidden; address@hidden;
>> address@hidden; address@hidden; address@hidden; address@hidden;
>> address@hidden; address@hidden
>> Subject: Re: [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads
>>
>> On 19/01/2018 13:25, Pavel Dovgalyuk wrote:
>>>>> It means, that I'll have to fix all the has_work function to avoid races,
>>>>> because x86_cpu_has_work may have them?
>>>> Why only x86_cpu_has_work?
>>>>
>>>> Even reading cs->interrupt_request outside the mutex is unsafe.
>>> All the vcpu function that access interrupt controller or peripheral state
>>> may be unsafe?
>>> How can it work safely then?
>>
>> They do it inside the big QEMU lock.
>
> Right. Without these patches.
> They are within the replay lock. And BQL is not covering vcpu execution with
> these patches.
> Therefore RR will be ok and regular execution may encounter races?
> It means that I missed something in Alex ideas, because he prepared the
> initial patches.
Yes.
>> But here you're calling cpu_has_work (via all_cpu_threads_idle) outside the
>> lock.
>
> Yes, I see, but what we have to do?
I don't know. But the idiom in these patches,
while(...) {
lock()
cond_wait()
unlock()
}
is unsafe as well, so the issue is more than just cpu_has_work.
Paolo
- Re: [Qemu-devel] [RFC PATCH v4 12/23] cpus: push BQL lock to qemu_*_wait_io_event, (continued)
- [Qemu-devel] [RFC PATCH v4 14/23] replay/replay.c: bump REPLAY_VERSION again, Pavel Dovgalyuk, 2018/01/19
- [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads, Pavel Dovgalyuk, 2018/01/19
- Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads, Paolo Bonzini, 2018/01/19
- Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads, Pavel Dovgalyuk, 2018/01/19
- Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads, Paolo Bonzini, 2018/01/19
- Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads, Pavel Dovgalyuk, 2018/01/19
- Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads, Paolo Bonzini, 2018/01/19
- Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads, Pavel Dovgalyuk, 2018/01/19
- Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads, Pavel Dovgalyuk, 2018/01/19
- Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads,
Paolo Bonzini <=
- Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads, Pavel Dovgalyuk, 2018/01/22
[Qemu-devel] [RFC PATCH v4 15/23] replay/replay-internal.c: track holding of replay_lock, Pavel Dovgalyuk, 2018/01/19
[Qemu-devel] [RFC PATCH v4 16/23] replay: make locking visible outside replay code, Pavel Dovgalyuk, 2018/01/19
[Qemu-devel] [RFC PATCH v4 17/23] replay: push replay_mutex_lock up the call tree, Pavel Dovgalyuk, 2018/01/19
[Qemu-devel] [RFC PATCH v4 18/23] replay: don't destroy mutex at exit, Pavel Dovgalyuk, 2018/01/19
[Qemu-devel] [RFC PATCH v4 20/23] replay: avoid recursive call of checkpoints, Pavel Dovgalyuk, 2018/01/19
[Qemu-devel] [RFC PATCH v4 19/23] replay: check return values of fwrite, Pavel Dovgalyuk, 2018/01/19
[Qemu-devel] [RFC PATCH v4 21/23] scripts/replay-dump.py: replay log dumper, Pavel Dovgalyuk, 2018/01/19
[Qemu-devel] [RFC PATCH v4 22/23] replay: don't process async events when warping the clock, Pavel Dovgalyuk, 2018/01/19
[Qemu-devel] [RFC PATCH v4 23/23] replay: save vmstate of the asynchronous events, Pavel Dovgalyuk, 2018/01/19