G. Varghese and T. Lauck, "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility," in The Proceedings of the  Home/Search   Document Not in Database   Summary   Related Articles   Check

....to be executed. The sending of a primitive implies sending the identifier of the receiver task to the task scheduler queue. When a task is executed, data from a specific instance are accessed through a index. Timer Management The Timer Manager implementation follows Varghese and Lauck proposal [16], where an analogy with a real clock is simulated by a cyclic counter. This implementation proved to be very efficient, avoiding unnecessary logical checks at each hardware interrupt, thus allowing the creation of a great number of run time timers. Figure 1: Implementation Architecture for the ....

G. Varghese and T. Lauck, "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility", in Proc. 11th ACM SIGOPS, Texas, 87.

....a entry point of lower priority tasks. b entry point of higher priority tasks. c entry point of maximum priority tasks and output of all the tasks. Figure 7: Task scheduler module. The timer manager module proved to be very efficient. It is based on the Varghese Lauck proposal [16], where an analogy with a real time clock is simulated by a cyclic counter. This implementation privileges the performance, avoiding unnecessary logical checks at each hardware interrupt, allowing the creation of a great number of run time timers dynamically. It provides functions to create simple ....

G. Varghese, T. Lauck, "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility", in Proc. 11th ACM SIGOPS Symp. on Operating Systems Principles, pp. 25-38, Austin, TX, 1987.

....uma rotina principal que checava se as filas da interface estavam no vazias, isto , se havia algum elemento (primitiva de servio) a ser processado. Este procedimento consumia muito tempo de processamento. Uma grande melhoria no desempenho foi atingida com a criao de um mdulo Escalonador de Tarefas [11]. Este mdulo consiste em uma fila nica que armazena a seqncia de tarefas a serem executadas. As medidas tambm incluem o overhead introduzido pelos cabealhos das camadas inferiores. Este overhead atinge 33 octetos para o usurio da camada Apresentao. De fato, as medidas so limites inferiores de ....

G. Varghese e T. Lauck, "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility", in Proc. 11th ACM SIGOPS Symp. on Operating Systems Principles, Austin, TX, 1987, pp. 25-38. Os resultados de vazo so satisfatrios e se encaixam bem em muitas das aplicaes industriais atuais.

.... An application may have several active contexts in the same time (several point to point associations with different application entities) The application examines the list of active contexts to determine the next context to be processed and the corresponding wait timer value as described in [33]. High Performance Implementation of Communication Subsystems 9 Buffer management The allocation of memory buffers is performed by the application. The sizes of the maximum receive or send buffers are specified in the corresponding fields in the control bloc structure. These buffers are directly ....

G. Varghese, T. Lauck, Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility. Proceedings of the 11 th ACM symposium on Operating Systems Principles, ACM Operating Systems Review, Austin, TX, November 1987.

....with the xtp timer init( function to determine the next active context to be processed and the timer value: the active list is examined sequentially and the context with the earliest event date will be chosen. This technique allows to avoid complex sort procedures after each event as detailed in [7]. 2.4.6 Error Control The error control procedures within XTP are designed to facilitate reliable data transfer. The procedures provide error detection and recovery in several ways: 1) by removing old or duplicate packets, 2) by monitoring the data transfer for data loss, 3) by protecting ....

G. Varghese, T. Lauck, Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility. Proceedings of the 11 th ACM symposium on Operating Systems Principles, ACM Operating Systems Review, Austin, TX, November 1987.

.... An application may have several active contexts in the same time (several point to point associations with different application entities) The application examines the list of active contexts to determine the next context to be processed and the corresponding wait timer value as described in [Var87]. Buffer management The allocation of memory buffers is performed by the application. The sizes of the maximum receive or send buffers are specified in the corresponding fields in the control bloc structure. These buffers are directly used by the application to compute process data. There is no ....

G. Varghese, T. Lauck. "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility", In Proceedings of the 11 th ACM symposium on Operating Systems Principles, Austin, TX, November 1987.

....of time in the future, which should be sufficient for RSVP. In order to accommodate the rare event that timers exceed this time horizon, an additional sorted list is kept and timers from this list are moved into the respective slot when it becomes available. This concept is known as a timer wheel [18]. The access complexity of such an implementation is O(log(n) with n being the (varying) number of timers in a slot. Consequently, performance of this container can be traded off against memory requirements by choosing the size and number of slots. This data structure design is shown in Figure ....

G. Varghese and A. Lauck. Hashed and hierarchical timing wheels: Data structures for the efficient implementation of a timer facility. Operating Systems Review Special Issue: Proceedings of the Eleventh Symposium on Operating Systems Principles, Austin, TX, USA, 21(5):25--38, November 1987.

....the FSMs. 4.3 Timer Component Several protocol functions, such as retransmission, reassembly, and connection management, require timer operations. In most implementations architectures, timers are supported by the operating system. However, this support often forms a major performance bottleneck [10]. Therefore, the modular VLSI implementation architecture comprises a dedicated timer component. According to the performance needs either this component can be scaled or several identical components can be implemented. The timer component (cf. Figure 4) manages a dynamic list of timers. Several ....

Varghese, G; Lauck, T.; Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility; ACM, 1987, pp. 25-38

.... GRANULARITY OF PROCESSES AND TASKS LAYER PARALLELISM CONNECTIONAL PARALLELISM MESSAGE PARALLELISM TASK PARALLELISM FINE GRAIN Figure 6: Relationship Between Process Architecture and Parallelism Granularity Different event management mechanisms include delta lists [30] timing wheels [31], and heap based [32] and list based [8] callout queues. The following two dimensions differentiate these mechanisms: 1) Search Structure ADT: Several data structures are commonly used to implement the different event management ADT mechanisms. One simple approach sorts the events by their ....

.... software components, including a message manager (an abstract data type that encapsulates messages exchanged between session and protocol objects) a map manager (used for demultiplexing incoming messages between adjacent protocols and sessions) and an event manager (based upon timing wheels [31] and used for timer driven activities like TCP s adaptive retransmission algorithm) In addition, the x kernel provides a standard library of microprotocols, which are reusable, modular software components that implement services common to many network protocols. These services include sliding ....

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G. Varghese and T. Lauck, "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility," in The Proceedings of the 11th Symposium on Operating System Principles, November 1987.

....heap is stored in absolute time units, e.g. as generated by the UNIX gettimeofday system call. Virtual methods are used in the ACE Timer Queue interface. Thus, applications can extend the default ACE implementation to support alternative data structures such as delta lists [11] or timing wheel [12]. Delta lists store time in relative units represented as offsets or deltas from the earliest ACE Time Value at the front of the list. Timing wheels use a circular buffer that makes it possible to start, stop, and maintain timers within the range of the wheel in O#1# time. The ACE framework ....

G. Varghese and T. Lauck, "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility," in The Proceedings of the 11 th Symposium on Operating System Principles, November 1987.

....the performance of the system. Instead, we decided to aggregate requests into sets of requests that arrive at a proximity of 15 millisecond of each other. These requests are kept in a cyclic set of queues, such that every request is inserted into the current queue, similarly to what is done in [17]. See illustration in Figure 3. Then, every 15 milliseconds, a sweeper task scans the last queue, i.e. the one that follows the current queue, reissues all the requests which are held in this queue and for which a reply has not arrived yet, and then assigns the last queue to be the new current ....

G. Varghese and T. Lauck. Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility. In Proc. of the 11th ACM Symposium on Operating Systems Principles, pages 25--38, Austin, Texas, November 1987. 17

....machine execution is also easily obtained. 3.5 Timer Management Protocol implementation includes timer based procedures which are used in error recovery routines, connection establishment and release time out control, etc. The Timer Manager implementation follows Varghese and Lauck proposal [20], where an analogy with a real clock is simulated by a cyclic counter. This implementation proved to be very efficient, avoiding unnecessary logical checks at each hardware interrupt, thus allowing the creation of a great number of run time timers. In the implemented architecture, a time out is ....

G. Varghese and T. Lauck, "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility", in Proc. 11th ACM SIGOPS Symp. on Operating Systems Principles, Austin, TX, 1987, pp. 25-38.

....in a later section. Note that another use for events is to perform periodic maintenance functions, such as garbage collection. This section introduces the interface to the x kernel s event manager, which allows protocols to schedule a procedure that is to be called after a period of time. See [6] for a description of the algorithm and data structures that underly the event manageer. The event manager defines a single object the Event and the following operation: Event evSchedule(EvFunc function, void argument, int time) This operation schedules an event that executes the ....

G. Varghese and T. Lauck. Hashed and hierarchical timing wheels: Data structures for the efficient implementation of a timer facility. In Proceedings of the Eleventh ACM Symposium on Operating Systems Principles, pages 25--38, Nov. 1987. 42

....trigger states frequently enough to allow the scheduling of softtimer events at a granularity of tens of secs. 1 In some architectures (e.g. Pentium) TLB misses are handled in hardware; in these machines, TLB faults cannot be used as trigger states. 2 A modified form of timing wheels [24] is used to maintain scheduled soft timer events. Example of minimum Event Time (just larger than T=1) Example of maximum Event Time (just smaller than T X 1=4) event fires event scheduled event scheduled event fires Time interrupt clock tick measuring clock tick Figure 1. Lower and upper bounds ....

G. Varghese and A. Lauck. Hashed and hierarchical timing wheels: Data structures for the efficient implementation of a timer facility. In Proceedings of the Eleventh ACM Symposium on Operating Systems Principles, pages 171--180, Austin, TX, Nov. 1987.

....labeled Original . The numbers indicate that with the new implementation, the overhead of the TCP timers becomes negligible and the available CPU cycles are converted into a throughput improvement of 25 by the Apache webserver. For the purpose of comparison, we also implemented a timing wheel[26] based approach for the management of TCP timers. Our results indicate that our list based implementation outperforms the timing wheel implementation by about 5 . This is because the setting and cancellation of events in a timing wheel involves pointer manipulations and the computation of a hash ....

G. Varghese and A. Lauck, "Hashed and hierarchical timing wheels: Data structures for the efficient implementation of a timer facility," in Proceedings of the Eleventh ACM Symposium on Operating Systems Principles, Nov. 1987, pp. 171--180.

....interrupt whichever is efficiently supported by the OS. A designated function in the TCP module is invoked as a result of the software interrupt. This function is used by the TCP module to implement its various event timer facilities using appropriate data structure, such as timing 9 wheel [24] and calendar queues [8] Again, the TCP module can query the granularity of this event service, and this granuarity determines the granularity of TCP s timers. Typically, the OS service for measuring time can provide a finer granularity than the service for event scheduling. This is because most ....

G. Varghese and A. Lauck. Hashed and hierarchical timing wheels: Data structures for the efficient implementation of a timer facility. In Proceedings of the Eleventh ACM Symposium on Operating Systems Principles, pages 171--180, Nov. 1987. 22

....call itself recursively. To handle this recursion, counting locks are used, so that if a thread already owns the lock, it simply increments a count and proceeds. Similarly, an unlock decrements the count, and the lock is released when the count reaches zero. The event manager uses a timing wheel [121] to manage events which are to occur in the future. The wheel is essentially another chained bucket hash table, where the hashing function is based on the time that the event is scheduled to run. To protect this structure, we added per chain locks, so that concurrent updates to the table were less ....

Varghese, G. and Lauck, T. Hashed and hierarchical timing wheels: Data structures for the efficient implementation of a timer facility. In The Proceedings of the 11th Symposium on Operating System Principles, November 1987.

....by a priority queue algorithm [4] The operations schedule event and get next event are modelled by the INSERT and EXTRACT MIN operations in the priority queue respectively. The priority queue implementation being originally used in the simulator was Timing Wheels based on Scheme 5 described in [13]. In Section 4.3.1 we describe this implementation and the problems associated with it. In Section 4.3.2, we describe a Calendar Queue [3] based priority queue. In Section 4.3.3, we present our improvements to the Calendar Queue algorithm. 10 4.3.1 Timing Wheels 0 1 2 3 12 12 19 24 6 Figure 5: ....

G. Varghese and A. Lauck. Hashed and hierarchical timing wheels: Data structures for the efficient implementation of a timer facility. In Proceedings of the Eleventh ACM Symposium on Operating Systems Principles, pages 171--180, Nov. 1987.

....the timer expires generating its own interrupt and alerting the driver of the error. Such use of watchdog timers is common in nearly all device drivers. Researchers have recognized the importance of reducing the overhead associated with timer management and developed efficient implementations. Varghese Lauck 87] During periods of high transmit activity, the driver may set the watchdog timer to expire in ten seconds, thousands of times a second. This would seem unnecessary. It is, of course, not important that the timer expire in exactly ten seconds. Rather, this number has been chosen somewhat ....

Vargheese. G. and Lauck, T. "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of Timer Facility." In Proceedings of the Eleventh ACM Symposium on Operating System Principles (Austin, TX. Nov. 8-11). ACM Press, New York, NY, 1987, pp. 25-38.

....that the new callout implementations using timing wheels take constant time. By contrast, the traditional BSD implementation takes time that increases linearly with the number of outstanding callouts. 8 Later Work A preliminary version of the work described in this paper was first described in [25]. Since then, a number of systems have built timer implementations based on this approach, and there have been a few extensions of the basic approach. Systems that use Timing Wheels: Some well known network protocol implementations have used the timing wheel ideas described in this paper. These ....

G. Varghese and A. Lauck. Hashed and hierarchical timing wheels: Data structures for the efficient implementation of a timer facility. Proceedings of the 11th ACM Symposium on Operating Systems Principles, pages 171--180, November 1987.

No context found.

G. Varghese and T. Lauck, "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility," in The Proceedings of the

No context found.

George Varghese and Anthony Lauck. Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility. Operating Systems Review Special Issue: Proceedings of the Eleventh Symposium on Operating Systems Principles, Austin, TX, USA, 21(5):25--38, November 1987.

No context found.

VARGHESE,G.AND LAUCK, A. 1987. Hashed and hierarchical timing wheels: Data structures for the efficient implementation of a timer facility. In Proceedings of the 11th ACM Symposium on Operating Systems Principles. ACM, New York, 171--180.

No context found.

G. Varghese, T. Lauck, "Hashed and Hierarchical Timing Wheels: Data Structures for the Efficient Implementation of a Timer Facility", ACM SIGOPS, pp. 25-38, Texas, 1987.

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Varghese, G.; Lauck, T.: Hashed and Hierarchical Timing Wheels: Data Strucutres for the Efficient Implementation of a Timer Facility, ACM, 1987, pp. 25-38

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