[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <D3E216785288A145B7BC975F83A2ED103FE40085@szxeml556-mbx.china.huawei.com>
Date: Sat, 4 May 2013 09:25:50 +0000
From: "Zhanghaoyu (A)" <haoyu.zhang@...wei.com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: kvm list <kvm@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
qemu-devel <qemu-devel@...gnu.org>,
Luonengjun <luonengjun@...wei.com>,
Zanghongyong <zanghongyong@...wei.com>,
"Huangweidong (C)" <weidong.huang@...wei.com>,
Qinchuanyu <qinchuanyu@...wei.com>
Subject: Re: KVM VM(rhel-5.5) %si is too high when TX/RX packets
>> 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.
>
>RHEL 5.5 is a very old update. Can you try RHEL 5.9?
>
>In any case, this looks a lot like a bug in the version of the driver that was included in RHEL5.5; you should contact Red Hat support services if you can still reproduce it with the latest RHEL5 update.
>
>Paolo
One patch has been proposed to QEMU, shown as below,
[PATCH] [KVM] Needless to update msi route when only msi-x entry "control" section changed
With regard to old version linux guest(e.g., rhel-5.5), in ISR processing, mask and unmask msi-x vector 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 RCU needed after updating routing table, so much time consumed for waiting in wait_rcu_gp(). So CPU usage in VM is so high, while from the view of host, VM's total CPU usage is so low.
Masking/unmasking msi-x vector only set msi-x entry "control" section, needless to update VM irq routing table.
hw/i386/kvm/pci-assign.c | 3 +++
1 files changed, 3 insertions(+)
--- a/hw/i386/kvm/pci-assign.c 2013-05-04 15:53:18.000000000 +0800
+++ b/hw/i386/kvm/pci-assign.c 2013-05-04 15:50:46.000000000 +0800
@@ -1576,6 +1576,8 @@ static void assigned_dev_msix_mmio_write
MSIMessage msg;
int ret;
+ /* Needless to update msi route when only msi-x entry "control" section changed */
+ if ((addr & (PCI_MSIX_ENTRY_SIZE - 1)) != PCI_MSIX_ENTRY_VECTOR_CTRL){
msg.address = entry->addr_lo |
((uint64_t)entry->addr_hi << 32);
msg.data = entry->data; @@ -1585,6 +1587,7 @@ static void assigned_dev_msix_mmio_write
if (ret) {
error_report("Error updating irq routing entry (%d)", ret);
}
+ }
}
}
}
Thanks,
Zhang Haoyu
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists