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From: Ingo Molnar <mingo@elte.hu>
To: Asias He <asias.hejun@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	Rusty Russell <rusty@rustcorp.com.au>,
	Mark McLoughlin <markmc@redhat.com>,
	Anthony Liguori <aliguori@us.ibm.com>,
	Pekka Enberg <penberg@kernel.org>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Sasha Levin <levinsasha928@gmail.com>,
	Prasad Joshi <prasadjoshi124@gmail.com>,
	kvm@vger.kernel.org
Subject: Re: [PATCH 1/2] kvm tools: Respect ISR status in virtio header
Date: Sat, 7 May 2011 16:00:30 +0200	[thread overview]
Message-ID: <20110507140030.GA2859@elte.hu> (raw)
In-Reply-To: <4DC529E8.8030104@gmail.com>


* Asias He <asias.hejun@gmail.com> wrote:

> BTW. The ping latency was caused by the movement of irq injection outside the 
> loop. Suppose we have 5 available buffers and only 1 buffer from tap device. 
> We will sleep on read without giving the buffer from tap to guest. The 
> latency will be huge in this case.
> 
>   while(virt_queue__available(vq)) {
> 	...
> 	read(tap_fd)
> 	...
>    }
>    trigger_irq()

But ... in one of the mails one of you claimed that even when moving the irq 
notification inside the loop (which we all agreed was necessary to avoid 
latencies!) the latencies would still occur during stress-tests.

So something is still not understood here and could hit us anytime with any of 
the virtio drivers in the future and such bugs are not always so nice to debug 
like the latency problem here ...

Thanks,

	Ingo

  reply	other threads:[~2011-05-07 14:00 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-07  2:34 [PATCH 1/2] kvm tools: Respect ISR status in virtio header Asias He
2011-05-07  2:34 ` [PATCH 2/2] kvm tools: Respect VRING_AVAIL_F_NO_INTERRUPT Asias He
2011-05-07  7:55   ` Ingo Molnar
2011-05-07  9:03     ` Pekka Enberg
2011-05-07 11:25       ` Asias He
2011-05-07  9:30 ` [PATCH 1/2] kvm tools: Respect ISR status in virtio header Ingo Molnar
2011-05-07 10:34   ` Sasha Levin
2011-05-07 10:39     ` Pekka Enberg
2011-05-07 10:39     ` Asias He
2011-05-07 11:15   ` Asias He
2011-05-07 14:00     ` Ingo Molnar [this message]
2011-05-07 14:24       ` Asias He
2011-05-07 13:14   ` Anthony Liguori
2011-05-07 14:02     ` Ingo Molnar
2011-05-07 14:21       ` Anthony Liguori
2011-05-07 14:47         ` Ingo Molnar
2011-05-07 14:52           ` Pekka Enberg
2011-05-07 14:55             ` Ingo Molnar
2011-05-07 14:50     ` Pekka Enberg
2011-05-07 15:01       ` Anthony Liguori
2011-05-07 15:02         ` Pekka Enberg
2011-05-07 15:06           ` Ingo Molnar

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