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Re: [PATCH v1 0/2] Add timeout mechanism to qmp actions


From: Zhenyu Ye
Subject: Re: [PATCH v1 0/2] Add timeout mechanism to qmp actions
Date: Sat, 19 Sep 2020 10:22:16 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0

On 2020/9/18 22:06, Fam Zheng wrote:
> 
> I can see how blocking in a slow io_submit can cause trouble for main
> thread. I think one way to fix it (until it's made truly async in new
> kernels) is moving the io_submit call to thread pool, and wrapped in a
> coroutine, perhaps.
>

I'm not sure if any other operation will block the main thread, other
than io_submit().

> I'm not sure qmp timeout is a complete solution because we would still
> suffer from a blocked state for a period, in this exact situation before
> the timeout.

Anyway, the qmp timeout may be the last measure to prevent the VM
soft lockup.  Ideally, after your fix of io_submit, this mechanism will
never be triggered.

Thanks,
Zhenyu



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