Optimizing network performance in virtual machines

In recent years, there has been a rapid growth in the adoption of virtual machine technology in data centers and cluster environments. This trend towards server virtualization is driven by two main factors: the savings in hardware cost that can be achieved through the use of virtualization, and the increased flexibility in the management of hardware resources in a cluster environment. An important consequence of server virtualization is the negative impact it has on the networking performance of server applications running in virtual machines (VMs). In this thesis, we address the problem of efficiently virtualizing the network interface in Type-II virtual machine monitors. In the Type-II architecture, the VMM relies on a special, 'host' operating system to provide the device drivers to access I/O devices, and executes the drivers within the host operating system. Using the Xen VMM as an example of this architecture, we identify fundamental performance bottlenecks in the network virtualization architecture of Type-II VMMs. We show that locating the device drivers in a separate host VM is the primary reason for performance degradation in Type-II VMMs, because of two reasons: a) the switching between the guest and the host VM for device driver invocation, and, b) I/O virtualization operations required to transfer packets between the guest and the host address spaces. We present a detailed analysis of the virtualization overheads in the Type-II I/O architecture, and we present three solutions which explore the performance that can be achieved while performing network virtualization at three different levels: in the host OS, in the VMM, and in the NIC hardware. Our first solution consists of a set of packet aggregation optimizations that explores the performance achievable while retaining the Type-II I/O architecture in the Xen VMM. This solution retains the core functionality of I/O virtualization, including device driver execution, in the Xen 'driver domain'. With this set of optimizations, we achieve an improvement by a factor of two to four in the networking performance of Xen guest domains. In our second solution, we move the task of I/O virtualization and device driver execution from the host OS to the Xen hypervisor. We propose a new I/O virtualization architecture, called the TwinDrivers framework, which combines the performance advantages of Type-I VMMs with the safety and software engineering benefits of Type-II VMMs. (In a Type-I VMM, the device driver executes directly in the hypervisor, and gives much better performance than a Type-II VMM). The TwinDrivers architecture results in another factor of two improvements in networking performance for Xen guest domains. Finally, in our third solution, we describe a hardware based approach to network virtualization, in which we move the task of network virtualization into the network interface card (NIC). We develop a specialized network interface (CDNA) which allows guest operating systems running in VMs to directly access a private, virtual context on the NIC for network I/O, bypassing the host OS entirely. This approach also yields performance benefits similar to the TwinDrivers software-only approach. Overall, our solutions help significantly bridge the gap between the network performance in a virtualized environment and a native environment, eventually achieving network performance in a virtual machine within 70% of the native performance

A Comparative study between preoperative axillary lymph node status with postoperative histopathological diagnosis in operable cases of breast cancer

Breast cancer is one of the commonest cancers among the female population in India. It has a varied spectrum spectrum of presentation and when detected early, a curative surgery can be offered to the patient. The most important prognostic factor determining the local recurrence is the axillary lymph node status. Management of axilla in Brest cancer has evolved from a radical approach to more conservative approaches like Sentinel lymph node biopsy. This study encompasses patients diagnosed with early Breast cancer upto Stage IIb. All these patients were evaluated preoperatively with Clinical examination, Sonomammogram and subjected to Modified Radical Mastectomy with Adjuvant Chemotherapy. Preoperative axillary lymph node status were compared with the histopathological staging and the sensitivity and specificity of Clinical Breast examination and Sonomammogram were calculated and the latter was found to be superior. A specific subset of population with distinct characteristics in which no pathological axillary node metastasis was detected was defined. Thus a subgroup ideal for a conservative approach to axilla was identified and defined in this study

Factors influencing the provision and uptake of Visual Inspection with Acetic Acid (VIA) screening for cervical cancer among women accessing antenatal and postpartum care at a tertiary center in Blantyre, Malawi

Background Over 90% of cervical cancer mortality occurs in low and middle income countries where early screening and management services are not widely available. Malawi has the highest cervical cancer incidence and mortality rates globally. Visual Inspection with Acetic acid (VIA) is the screening of choice, management is limited to chemotherapy and palliative care. This dissertation describes factors associated with provision of VIA during antenatal (ANC) and postpartum (PPC) care, and with acceptance of VIA during PPC clinics. We also describe the sociodemographic and health characteristics of women with labia minora elongation (LME) and examine their uptake of maternal health interventions. Methods The study sampled 529 women at a tertiary center in Malawi attending either ANC (pregnant 28+ weeks), or PPC clinic (postpartum 6 weeks). We conducted descriptive statistics followed by logistic regression models to determine the impact of sociodemographic, obstetric, clinical and relationship factors on rates of VIA offer and uptake. Then, we described the sociodemographic and health correlates of women with LME and explored their likelihood of being offered select diagnostic and management interventions when accessing maternal care. Results Women attending PPC clinics were more likely (AOR=5.19, p<0.001) to be offered VIA when compared to ANC. Women who had no school through primary (AOR=0.55, p=0.04), those with LME (AOR=2.04; p=0.003) and with abnormal vaginal exam signs (AOR=0.33; p=0.06) were more likely to be offered VIA compared to their counterparts. Women reporting high degree of sexual satisfaction were less likely to refuse VIA in PPC clinic (AOR=0.34, p=0.02). Women with LME were more likely to be illiterate or partially literate (12.4% v/s 6.2%, p=0.03) and to have travelled more than 30 minutes to reach clinic (74.3% v/s 62.2% p=0.007). They were less likely to have undergone ultrasound exams (AOR=0.41, p=0.002) or to have had instrumentation (including cesarean section) during their most recent pregnancy or delivery (AOR=0.49, p=0.06). Conclusions Healthcare providers may be influenced by women’s sociodemographic, cultural and clinical characteristics while offering VIA screening during ANC/PPC clinics. Meanwhile, women’s sociodemographic background and personal attitudes seem to be linked to uptake of preventive, diagnostic and management interventions during ANC/PPC

TwinDrivers: Semi-Automatic Derivation of Fast and Safe Hypervisor Network Drivers from Guest OS Drivers

In a virtualized environment, device drivers are often run inside a virtual machine (VM) rather than in the hypervisor. Doing so protects the hypervisor from bugs in the driver, and also allows the reuse of the device driver and its support infrastructure in the VM. Unfortunately, this approach results in poor performance for I/O intensive devices such as network cards. The alternative approach is to run device drivers directly in the hypervisor. Although this approach results in better performance, it suffers from the loss of safety guarantees for the hypervisor, and incurs the software engineering cost of maintaining the driver support infrastructure. In this paper we present TwinDrivers, a framework which allows us to automatically create safe and efficient hypervisor drivers from guest OS drivers. The hypervisor driver runs directly in the hypervisor, but its data resides completely in the driver VM address space. A Software Virtual Memory mechanism allows the driver to access its VM data efficiently from the hypervisor running in any guest context, and also protects the hypervisor from invalid memory accesses from the driver. An upcall mechanism allows the hypervisor to largely reuse the driver support infrastructure present in the VM. The TwinDriver system thus combines the performance benefits of hypervisor-driver based approaches with the safety and software engineering benefits of VM driver based approaches. Using the TwinDrivers hypervisor driver, we are able to improve the guest domain networking performance in Xen by a factor of 2.4 for transmit workloads, and 2.1 for receive workloads. The resulting transmit perfomance is within 64% of native Linux performance, and the receive performance is within 67% of Linux performance

Optimizing Network Virtualization in Xen

BEST PAPER AWARDIn this paper, we propose and evaluate three techniques for optimizing network performance in the Xen virtualized environment. Our techniques retain the basic Xen architecture of locating device drivers in a privileged `driver' domain with access to I/O devices, and providing network access to unprivileged `guest' domains through virtualized network interfaces. First, we redefine the virtual network interfaces of guest domains to incorporate high-level network offfload features available in most modern network cards. We demonstrate the performance benefits of high-level offload functionality in the virtual interface, even when such functionality is not supported in the underlying physical interface. Second, we optimize the implementation of the data transfer path between guest and driver domains. The optimization avoids expensive data remapping operations on the transmit path, and replaces page remapping by data copying on the receive path. Finally, we provide support for guest operating systems to effectively utilize advanced virtual memory features such as superpages and global page mappings. The overall impact of these optimizations is an improvement in transmit performance of guest domains by a factor of 4.4. The receive performance of the driver domain is improved by 35% and reaches within 7% of native Linux performance. The receive performance in guest domains improves by 18%, but still trails the native Linux performance by 61%. We analyse the performance improvements in detail, and quantify the contribution of each optimization to the overall performance

Macrophage‐derived apoptotic bodies promote the proliferation of the recipient cells via shuttling microRNA‐221/222

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141103/1/jlb1349.pd

The HemQ coprohaem decarboxylase generates reactive oxygen species: implications for the evolution of classical haem biosynthesis

Bacteria require a haem biosynthetic pathway for the assembly of a variety of protein complexes including cytochromes, peroxidases, globins, and catalase. Haem is synthesised via a series of tetrapyrrole intermediates including non-metallated porphyrins such as protoporphyrin IX, which is well-known to generate reactive oxygen species (ROS) in the presence of light and oxygen. Staphylococcus aureus has an ancient haem biosynthetic pathway that proceeds via the formation of coproporphyrin III, a less reactive porphyrin. Herein, we demonstrate for the first time that HemY of S. aureus is able to generate both protoporphyrin IX and coproporphyrin III, and that the terminal enzyme of this pathway, HemQ, can stimulate the generation of protoporphyrin IX (but not coproporphyrin III). Assays with hydrogen peroxide, horseradish peroxidase, superoxide dismutase, and catalase confirm that this stimulatory effect is mediated by superoxide. Structural modelling reveals that HemQ enzymes do not possess the structural attributes that are common to peroxidases that form compound I [FeIV=O]+, which taken together with the superoxide data leaves Fenton chemistry as a likely route for the superoxide-mediated stimulation of protoporphyrinogen IX oxidase activity of HemY. This generation of toxic free radicals could explain why HemQ enzymes have not been identified in organisms that synthesise haem via the classical protoporphyrin IX pathway. This work has implications for the divergent evolution of haem biosynthesis in ancestral microorganisms and provides new structural and mechanistic insights into a recently discovered oxidative decarboxylase reaction

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy