From: Avi Kivity <avi@redhat.com>
To: Alexander Graf <agraf@suse.de>
Cc: "Jan Kiszka" <jan.kiszka@web.de>,
"Michael Tokarev" <mjt@tls.msk.ru>,
"René Pfeiffer" <lynx@luchs.at>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: I/O performance of VirtIO
Date: Sun, 25 Oct 2009 07:44:16 +0200 [thread overview]
Message-ID: <4AE3E5B0.5080700@redhat.com> (raw)
In-Reply-To: <7A331778-3227-43B1-B2E2-A6BE6F92C834@suse.de>
On 10/23/2009 12:06 AM, Alexander Graf wrote:
>
> Am 22.10.2009 um 18:29 schrieb Avi Kivity <avi@redhat.com>:
>
>> On 10/13/2009 08:35 AM, Jan Kiszka wrote:
>>> It can be particularly slow if you use in-kernel irqchips and the
>>> default NIC emulation (up to 10 times slower), some effect I always
>>> wanted to understand on a rainy day. So, when you actually want -net
>>> user, try -no-kvm-irqchip.
>>>
>>
>> This might be due to a missing SIGIO or SIGALRM; -no-kvm-irqchip
>> generates a lot of extra signals and thus polling opportunities.
>
> Isn't that what dedicated io threads are supposed to solve?
>
No. Dedicated I/O threads provide parallelism. All latency needs is to
have SIGIO sent on all file descriptors (or rather, in qemu-kvm with
irqchip, to have all file descriptors in the poll() call).
Jan, does slirp add new connections to the select set?
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
next prev parent reply other threads:[~2009-10-25 5:45 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-12 20:49 I/O performance of VirtIO René Pfeiffer
2009-10-12 21:45 ` Michael Tokarev
2009-10-12 21:54 ` René Pfeiffer
2009-10-13 6:35 ` Jan Kiszka
2009-10-22 16:29 ` Avi Kivity
2009-10-22 22:06 ` Alexander Graf
2009-10-25 5:44 ` Avi Kivity [this message]
2009-10-26 8:12 ` Jan Kiszka
2009-10-26 8:35 ` Avi Kivity
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