We also show that FastMap is able to saturate state-of-the-art fast storage devices when used by a large number of cores, where Linux mmap fails to scale. Additionally, it provides up to 5.27× higher throughput using an Optane SSD. A memory-mapped file I/O approach sacrifices memory usage for speed, which is classically called the spacetime tradeoff. Our experimental analysis shows that FastMap scales up to 80 cores and provides up to 11.8× more IOPS compared to mmap using null_blk. FastMap also increases device queue depth, an important factor to achieve peak device throughput. To overcome these limitations, we propose FastMap, an alternative design for the memory-mapped I/O path in Linux that provides scalable access to fast storage devices in multi-core servers, by reducing synchronization overhead in the common path. We show that the performance of Linux memory-mapped I/O does not scale beyond 8 threads on a 32-core server.
The following example creates a memory-mapped view of a part of an extremely large file and manipulates a portion of it. However, the Linux memory-mapped I/O path suffers from several scalability limitations. Memory-mapped I/O versus port-based I/O when interfacing things to microprocessors.An introductory explanation of memory mapped I/O versus port-based I/O use. The xref:System.IO.2A methods create a memory-mapped file from an existing file on disk.
Arithmetic or logic operation can be directly performed with I/O data. More hardware is required to decode 16-bit address. Memory-mapped I/O is an I/O scheme where the devices own on-board memory is mapped into the processors address space. The memory map (64K) is shared between I/O device and system memory. Memory-mapped I/O provides several potential advantages over explicit read/write I/O, especially for low latency devices: (1) It does not require a system call, (2) it incurs almost zero overhead for data in memory (I/O cache hits), and (3) it removes copies between kernel and user space. + Much much faster than IO mapped IO (100x)+ Huge address space compared to limited IO port space+ Most CPU memory addressing modes now available to IO space. - Data transfer between any general-purpose register and I/O port.
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