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From: Fam Zheng <fam@euphon.net>
To: Zhenyu Ye <yezhenyu2@huawei.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
	qemu-block@nongnu.org, qemu-devel@nongnu.org,
	xiexiangyou@huawei.com, armbru@redhat.com,
	Stefan Hajnoczi <stefanha@redhat.com>,
	pbonzini@redhat.com, mreitz@redhat.com
Subject: Re: [PATCH v1 0/2] Add timeout mechanism to qmp actions
Date: Mon, 21 Sep 2020 11:14:35 +0000	[thread overview]
Message-ID: <20200921111435.GA2524022@dev> (raw)
In-Reply-To: <1ba06b0d-3fcf-3676-f9e0-52875851ff19@huawei.com>

On 2020-09-19 10:22, Zhenyu Ye wrote:
> 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().

Then that's a problem with io_submit which should be fixed. Or more
precisely, that is a long held lock that we should avoid in QEMU's event
loops.

> 
> > 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. 

Maybe, but I don't think baking such a workaround into the QMP API is a
good idea. No QMP command should be synchronously long running, so
having a timeout parameter is just a wrong design.

Thanks,

Fam


  reply	other threads:[~2020-09-21 11:17 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-10 14:52 [PATCH v1 0/2] Add timeout mechanism to qmp actions Zhenyu Ye
2020-08-10 14:52 ` [PATCH v1 1/2] util: introduce aio_context_acquire_timeout Zhenyu Ye
2020-08-10 14:52 ` [PATCH v1 2/2] qmp: use aio_context_acquire_timeout replace aio_context_acquire Zhenyu Ye
2020-08-10 15:38 ` [PATCH v1 0/2] Add timeout mechanism to qmp actions Kevin Wolf
2020-08-11 13:54   ` Zhenyu Ye
2020-08-21 12:52     ` Stefan Hajnoczi
2020-09-14 13:27     ` Stefan Hajnoczi
2020-09-17  7:36       ` Zhenyu Ye
2020-09-17 10:10         ` Fam Zheng
2020-09-17 15:44         ` Stefan Hajnoczi
2020-09-17 16:01           ` Fam Zheng
2020-09-18 11:23             ` Zhenyu Ye
2020-09-18 14:06               ` Fam Zheng
2020-09-19  2:22                 ` Zhenyu Ye
2020-09-21 11:14                   ` Fam Zheng [this message]
2020-10-13 10:00                     ` Stefan Hajnoczi
2020-10-19 12:40                       ` Zhenyu Ye
2020-10-19 13:25                         ` Paolo Bonzini
2020-10-20  1:34                           ` Zhenyu Ye
2020-10-22 16:29                             ` Fam Zheng
2020-12-08 13:10                               ` Stefan Hajnoczi
2020-12-08 13:47                                 ` Glauber Costa
2020-12-14 16:33                                   ` Stefan Hajnoczi
2020-12-21 11:30                                     ` Zhenyu Ye
2020-09-14 14:42     ` Daniel P. Berrangé
2020-09-17  8:12       ` Zhenyu Ye
2020-08-12 13:51 ` Stefan Hajnoczi
2020-08-13  1:51   ` Zhenyu Ye

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