The Cache Manager never discards data from a file that has been modified locally but not yet stored back to the File Server. If the cache is very small, the Cache Manager possible cannot find any data to discard. For more information about the algorithm it uses when discarding cached data, see How the Cache Manager Chooses Data to Discard.
The amount of disk or memory you devote to caching depends on several factors. The amount of space available in memory or on the partition housing the disk cache directory imposes an absolute limit.
The afsd program exits without starting the Cache Manager and prints an appropriate message to the standard output stream if you violate this restriction. For a memory cache, you must leave enough memory for other processes and applications to run. If you try to allocate more memory than is actually available, the afsd program exits without initializing the Cache Manager and produces the following message on the standard output stream:. Within these hard limits, the factors that determine appropriate cache size include the number of users working on the machine, the size of the files with which they usually work, and for a memory cache the number of processes that usually run on the machine.
The higher the demand from these factors, the larger the cache needs to be to maintain good performance. Disk caches smaller than 10 MB do not generally perform well. Machines serving multiple users usually perform better with a cache of at least 60 to 70 MB. The point at which enlarging the cache further does not really improve performance depends on the factors mentioned previously, and is difficult to predict.
Memory caches smaller than 1 MB are nonfunctional, and the performance of caches smaller than 5 MB is usually unsatisfactory. Suitable upper limits are similar to those for disk caches but are probably determined more by the demands on memory from other sources on the machine number of users and processes.
Machines running only a few processes possibly can use a smaller memory cache. AFS imposes an absolute limit on cache size in some versions. To change any of the values in the file, log in as the local superuser root. You must reboot the machine to have the new value take effect. For instructions, see To edit the cacheinfo file. To change the cache size at reboot without editing the cacheinfo file, include the -blocks argument to the afsd command; see the command's reference page in the OpenAFS Administration Reference.
For a disk cache, you can also use the fs setcachesize command to reset the cache size without rebooting. The value you set persists until the next reboot, at which time the cache size returns to the value specified in the cacheinfo file or by the -blocks argument to the afsd command.
For instructions, see To change the disk cache size without rebooting. The L1 cache is usually split into two sections: the instruction cache and the data cache. The instruction cache deals with the information about the operation that the CPU must perform, while the data cache holds the data on which the operation is to be performed.
L2 Level 2 cache is slower than the L1 cache but bigger in size. Where an L1 cache may measure in kilobytes, modern L2 memory caches measure in megabytes. When it comes to speed, the L2 cache lags behind the L1 cache but is still much faster than your system RAM. The L1 memory cache is typically times faster than your RAM, while the L2 cache is around 25 times faster.
Onto the L3 Level 3 cache. In the early days, the L3 memory cache was actually found on the motherboard. This was a very long time ago, back when most CPUs were just single-core processors. The L3 cache is the largest but also the slowest cache memory unit. But while the L1 and L2 cache exist for each core on the chip itself, the L3 cache is more akin to a general memory pool that the entire chip can make use of.
Note how the L1 cache is split into two, while the L2 and L3 are bigger respectively. It's a good question.
More is better, as you might expect. The latest CPUs will naturally include more CPU cache memory than older generations, with potentially faster cache memory, too.
One thing you can do is learn how to compare CPUs effectively. There is a lot of information out there, and learning how to compare and contrast different CPUs can help you make the right purchasing decision. When the processor is looking for data to carry out an operation, it first tries to find it in the L1 cache.
If the CPU finds it, the condition is called a cache hit. It then proceeds to find it in L2 and then L3. When that happens, it is known as a cache miss. L1 cache — This is the primary cache. It is typically embedded in the processor chip.
L2 cache — Also known as secondary cache, L2 cache can either be embedded on the processor chip or on a separate chip with a high-speed bus that connects it to the CPU. L3 cache — This processor cache is specialized memory that can serve as a backup for your L1 and L2 caches. It may not be as fast, but it boosts the performance of your L1 and L2. Direct mapped cache — With this configuration, each block is mapped to one cache location, specified in advance.
Fully associative cache mapping — This configuration is like direct mapped cache in structure, but a block can be mapped to any location rather than to a specific cache location. Set associative cache mapping — This falls between the two extremes of direct-mapped and fully associative cache mapping. Although the mapping is prespecified, each block is mapped to a subset of various cache locations, rather than having only one designated. Cache memory is usually double the speed of DRAM.
Unlike DRAM, which has to be refreshed frequently, cache needs no refresh. Power your system down and remove the power cable. Unplug all other cables from the back of your computer.
Remove the side panel so that you can more easily get to the RAM slots inside your computer. Eject any RAM you currently have installed. Install the new RAM by lining up the edges with your motherboard slots and press them into place with a firm push. It should go in fairly easily this way. If not, it could be that you need to flip them around to the other side. Replace the side panel and reinsert all cables, including the power cable.
Boot your system up. Check to make sure the system is registering the new RAM amount. Related Articles.
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