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[Qemu-devel] [Bug 1686980] Re: qemu is very slow when adding 16, 384 vir
From: |
Daniel Berrange |
Subject: |
[Qemu-devel] [Bug 1686980] Re: qemu is very slow when adding 16, 384 virtio-scsi drives |
Date: |
Fri, 28 Apr 2017 14:08:54 -0000 |
I added further instrumentation and got this profile of where the
remaining time goes
1000x drive_new 18.347secs
-> 1000x blockdev_init 18.328secs
-> 1000x monitor_add_blk 4.515secs
-> 1000x blk_by_name 1.545secs
-> 1000x bdrv_find_node 2.968secs
-> 1000x blk_new_open 13.786secs
-> 1000x bdrv_open 13.783secs
These numbers are all increasing as we process more & more -drive args,
so there's some O(N) factor in blk_by_name, bdrv_find_node and bdrv_open
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https://bugs.launchpad.net/bugs/1686980
Title:
qemu is very slow when adding 16,384 virtio-scsi drives
Status in QEMU:
New
Bug description:
qemu runs very slowly when adding many virtio-scsi drives. I have
attached a small reproducer shell script which demonstrates this.
Using perf shows the following stack trace taking all the time:
72.42% 71.15% qemu-system-x86 qemu-system-x86_64 [.] drive_get
|
--72.32%--drive_get
|
--1.24%--__irqentry_text_start
|
--1.22%--smp_apic_timer_interrupt
|
--1.00%--local_apic_timer_interrupt
|
--1.00%--hrtimer_interrupt
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--0.83%--__hrtimer_run_queues
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--0.64%--tick_sched_timer
21.70% 21.34% qemu-system-x86 qemu-system-x86_64 [.]
blk_legacy_dinfo
|
---blk_legacy_dinfo
3.65% 3.59% qemu-system-x86 qemu-system-x86_64 [.] blk_next
|
---blk_next
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