Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751641Ab3EDEHA (ORCPT ); Sat, 4 May 2013 00:07:00 -0400 Received: from szxga01-in.huawei.com ([119.145.14.64]:21433 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750921Ab3EDEG6 convert rfc822-to-8bit (ORCPT ); Sat, 4 May 2013 00:06:58 -0400 From: "Zhanghaoyu (A)" To: "Zhanghaoyu (A)" , kvm list , "linux-kernel@vger.kernel.org" , qemu-devel CC: Qinchuanyu , "Huangweidong (C)" , Zanghongyong , Luonengjun Subject: Re: KVM VM(rhel-5.5) %si is too high when TX/RX packets Thread-Topic: KVM VM(rhel-5.5) %si is too high when TX/RX packets Thread-Index: Ac5Hs1wISEMZKpucRUKMj7M5PG0M3gAxJBQw Date: Sat, 4 May 2013 04:06:39 +0000 Message-ID: References: In-Reply-To: Accept-Language: zh-CN, en-US Content-Language: zh-CN X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.135.68.97] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2057 Lines: 21 > I running a VM(RHEL-5.5) on KVM hypervisor(linux-3.8 + QEMU-1.4.1), and direct-assign intel 82576 VF to the VM. When TX/RX packets on VM to the other host via iperf tool, top tool result on VM shown that the %si is too high, approximately 95% ~ 100%, but from the view of host, the VM's total CPU usage is about 20% - 30%. And the throughput rate is approximately 200Mb/s, far from the line rate 1Gb/s, And, I found the hardirq rate is lower than normal by running "watch -d -n 1 cat /proc/interrupts", I think it's caused by the too high %si, because the NIC's hardirq was disabled during the softirq process. > Then, I direct-assign the intel 82576 to the VM, the same case happened too. > I found the intel 82576 and intel 82576 VF's interrupt mode are both PCI-MSI-X. > > And, > I rmmod the igb driver, and, re-insmod the igb driver(igb-4.1.2) with the parameter IntMode=0/1(0:legacy, 1:MSI, 2:MSI-x), the problem then gone, the %si is approximately 20% -30%, and the throughput rate came to the line rate, about 940Mb/s. > I update the VM to RHEL-6.1, the problem disappeared too. > And, I found a very strange thing, the VM's 82576VF's irq routing is set one time on Vf's one interrupt received, so frequently. With regard to rhel-5.5(linux-2.6.18), in ISR process, mask and unmask msi-x vector function msi_set_mask_bit() was invoked every time, which result in VMEXIT, then QEMU will invoke kvm_irqchip_update_msi_route() to ask KVM hypervisor to update the VM irq routing table. In KVM hypervisor, synchronizing process needed after updating routing table, so much time consumed for waiting in wait_rcu_gp(). So %si in VM is so high, while from the view of host, VM's total CPU usage is so low. Why in ISR process, masking and unmasking msi-x vector is needed every time? Thanks, Zhang Haoyu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/