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From: Stefan Hajnoczi <stefanha@redhat.com>
To: "Wangkai (Kevin,C)" <wangkai86@huawei.com>
Cc: Lee yang <lee.yang@huawei.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"aliguori@amazon.com" <aliguori@amazon.com>
Subject: Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap
Date: Fri, 11 Jul 2014 15:04:13 +0200	[thread overview]
Message-ID: <20140711130413.GA4255@stefanha-thinkpad.redhat.com> (raw)
In-Reply-To: <87B246BB5ED53A4C98E4F9A35839EDE128F6F49D@nkgeml506-mbs.china.huawei.com>

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On Fri, Jul 11, 2014 at 01:05:30AM +0000, Wangkai (Kevin,C) wrote:
> When used a tap as net driver for vm, if too many packets was delivered to the 
> guest os via tap interface, the guest os will be blocked on io events for a long
> time, while tap driver was busying process packets.
> 
> kvm vcpu thread block on io lock call trace:
>   __lll_lock_wait
>   _L_lock_1004
>   __pthread_mutex_lock
>   qemu_mutex_lock
>   kvm_cpu_exec
>   qemu_kvm_cpu_thread_fn
>   start_thread
> 
> qemu io thread call trace:
>   ...
>   qemu_net_queue_send
>   tap_send
>   qemu_iohandler_poll
>   main_loop_wait
>   main_loop
>   
> 
> I think the qemu io lock time should be as small as possible, and the io work
> slice should be limited at a particular ration or time.
> 
> ---
> Signed-off-by: Wangkai <wangkai86@huawei.com>

How many packets are you seeing in a single tap_send() call?

Have you profiled the tap_send() code path?  Maybe it is performing some
operation that is very slow.

By the way, if you want good performance you should use vhost_net
instead of userspace vhost_net.  Userspace virtio-net is not very
optimized.

Stefan

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  reply	other threads:[~2014-07-11 13:04 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-07-11  1:05 [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap Wangkai (Kevin,C)
2014-07-11 13:04 ` Stefan Hajnoczi [this message]
2014-07-14  1:55   ` Wangkai (Kevin,C)
2014-07-14  8:43     ` Stefan Hajnoczi
2014-07-14 10:44       ` Wangkai (Kevin,C)
2014-07-15 14:59         ` Stefan Hajnoczi
2014-07-16 10:10           ` Wangkai (Kevin,C)
2014-07-17  3:43           ` Wangkai (Kevin,C)
2014-07-17  5:36             ` Jason Wang
2014-07-17  7:48               ` Wangkai (Kevin,C)
2014-07-17 12:54 ` Stefan Hajnoczi

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