From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=37325 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PrS5d-0004Va-Jj for qemu-devel@nongnu.org; Mon, 21 Feb 2011 04:29:58 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PrS5c-00014y-Di for qemu-devel@nongnu.org; Mon, 21 Feb 2011 04:29:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51357) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PrS5c-00014r-6I for qemu-devel@nongnu.org; Mon, 21 Feb 2011 04:29:56 -0500 Message-ID: <4D62308D.1070101@redhat.com> Date: Mon, 21 Feb 2011 11:29:49 +0200 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: How can I understand CONFIG_IO_THREAD ? References: <4D621F77.3080802@redhat.com> In-Reply-To: <4D621F77.3080802@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: wang sheng , qemu-devel@nongnu.org On 02/21/2011 10:16 AM, Paolo Bonzini wrote: > On 02/21/2011 04:13 AM, wang sheng wrote: >> What is the purpose of io_thread desigment in qemu ? > > There was a lengthy thread recently explaining how it helps fixing a > possibly delay in handling I/O. It is also useful for KVM, where you > have one I/O thread and multiple CPU threads. This way, KVM can > implement "real" SMP (i.e. multiple virtual CPUs running concurrently). > In fact kvm smp was available even before the iothread; one thread handled both vcpu 0 and I/O completions, while the other threads only handled a vcpu each. Later, the first thread was split into an iothread and a vcpu 0 thread. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.