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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, armbru@redhat.com, xiexiangyou@huawei.com,
	qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>,
	pbonzini@redhat.com, mreitz@redhat.com
Subject: Re: [PATCH v1 0/2] Add timeout mechanism to qmp actions
Date: Fri, 18 Sep 2020 14:06:28 +0000	[thread overview]
Message-ID: <20200918140628.GA2509473@dev> (raw)
In-Reply-To: <5a5822ec-f3bc-a247-2b5a-f764b941c820@huawei.com>

On 2020-09-18 19:23, Zhenyu Ye wrote:
> 	Thread 5 (LWP 4802):
> 	#0  0x0000ffff83086b54 in syscall () at /lib64/libc.so.6
> 	#1  0x0000ffff834598b8 in io_submit () at /lib64/libaio.so.1
> 	#2  0x0000aaaae851e89c in ioq_submit (s=0xfffd3c001bb0) at ../block/linux-aio.c:299
> 	#3  0x0000aaaae851eb50 in laio_io_unplug (bs=0xaaaaef0f2340, s=0xfffd3c001bb0)
> 	    at ../block/linux-aio.c:344
> 	#4  0x0000aaaae8559f1c in raw_aio_unplug (bs=0xaaaaef0f2340) at ../block/file-posix.c:2063
> 	#5  0x0000aaaae8538344 in bdrv_io_unplug (bs=0xaaaaef0f2340) at ../block/io.c:3135
> 	#6  0x0000aaaae8538360 in bdrv_io_unplug (bs=0xaaaaef0eb020) at ../block/io.c:3140
> 	#7  0x0000aaaae8496104 in blk_io_unplug (blk=0xaaaaef0e8f20)
> 	    at ../block/block-backend.c:2147
> 	#8  0x0000aaaae830e1a4 in virtio_blk_handle_vq (s=0xaaaaf0374280, vq=0xffff700fc1d8)
> 	    at ../hw/block/virtio-blk.c:796
> 	#9  0x0000aaaae82e6b68 in virtio_blk_data_plane_handle_output
> 	    (vdev=0xaaaaf0374280, vq=0xffff700fc1d8) at ../hw/block/dataplane/virtio-blk.c:165
> 	#10 0x0000aaaae83878fc in virtio_queue_notify_aio_vq (vq=0xffff700fc1d8)
> 	    at ../hw/virtio/virtio.c:2325
> 	#11 0x0000aaaae838ab50 in virtio_queue_host_notifier_aio_poll (opaque=0xffff700fc250)
> 	    at ../hw/virtio/virtio.c:3545
> 	#12 0x0000aaaae85fab3c in run_poll_handlers_once
> 	    (ctx=0xaaaaef0a87b0, now=77604310618960, timeout=0xffff73ffdf78)
> 	    at ../util/aio-posix.c:398
> 	#13 0x0000aaaae85fae5c in run_poll_handlers
> 	    (ctx=0xaaaaef0a87b0, max_ns=4000, timeout=0xffff73ffdf78) at ../util/aio-posix.c:492
> 	#14 0x0000aaaae85fb078 in try_poll_mode (ctx=0xaaaaef0a87b0, timeout=0xffff73ffdf78)
> 	    at ../util/aio-posix.c:535
> 	#15 0x0000aaaae85fb180 in aio_poll (ctx=0xaaaaef0a87b0, blocking=true)
> 	    at ../util/aio-posix.c:571
> 	#16 0x0000aaaae8027004 in iothread_run (opaque=0xaaaaeee79a00) at ../iothread.c:73
> 	#17 0x0000aaaae85f269c in qemu_thread_start (args=0xaaaaef0a8d10)
> 	    at ../util/qemu-thread-posix.c:521
> 	#18 0x0000ffff831428bc in  () at /lib64/libpthread.so.0
> 	#19 0x0000ffff8308aa1c in  () at /lib64/libc.so.6

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 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.

Fam


  reply	other threads:[~2020-09-18 14:08 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 [this message]
2020-09-19  2:22                 ` Zhenyu Ye
2020-09-21 11:14                   ` Fam Zheng
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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