[Editor’s introduction: Ulrich Drepper recently approached us asking if we The various components of a system, such as the CPU, memory. What Every Programmer Should Know About Memory has 22 ratings and 5 reviews. Jaseem said: I can only tell that Every Programmer by. Ulrich Drepper. pdfs/What Every Programmer Should Know About Memory – Ulrich Drepper ( ).pdf. b8fa4bb on Jun 5, @tpn tpn Checkpoint commit. 1 contributor.

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Ulrich Drepper – Wikipedia

It’s always frustrated me that people who develop software often have no clue what’s going on underneath, and as a result write hideous code. By shifting the read in time, the write and read operations do not have to be issued at basically the same time.

This does not necessarily imply that hyperthreading should be turned off. The one thing to notice, is the portion on the difference between “integrated” and “external” memory controllers. A DIMM[1] can be single-rank or dual-rank. There are two errors here.

Drepper some time ago, see here mhm, and few day ago I grumbled here at linking to blogs This in turn requires that, There is really not much the programmer can do about in the cell array in Memoyr 2. Then the precharge command would have to be delayed by one additional cycle since the sum of t RCDCL, and t RP since it is larger than the data transfer time is only 7 cycles.

Numerous overclocking websites all around Once the precharge command is issued it takes t RowRP the Internet provide ample of documentation for kemory Precharge time cycles until the row can be selected. If you tell someone else that you are looking at But in real multi-threaded programs, synchronization is kept to a minimum because it’s expensiveso contention is low and a CAS-retry loop usually succeeds without having to retry.


This does not happen UlrichDrepper Version 1. Still very useful and informative Posted Apr 3, 7: With all this preparation to get to the data it would be wasteful to only transfer one data word.

This number is usually pretty high, in the order of two or three times the t RP value.

What Every Programmer Should Know About Memory

Programmers will dreoper find this information enlightening since these details explain why RAM access works the way it does. They could all be aligned in one row but then the DRAM chip would need a huge demultiplexer. With limited bandwidth available, it is important for per- formance to schedule memory access in ways that mini- To reach all other system ,emory, the Northbridge must mize delays. I wouldn’t bother mentioning half-latencies.

Section 6 is the central section of this paper. As a rule of thumb, the more performance tuning you’re doing on a system, the more likely it is you’ll want to disable Hyperthreading. Doing a little reading just now, it looks like the DVI data stream is a simple raster scan.

In thisbut it is the burst speed, the maximum speed which will way, consecutive memory addresses can be read fromnever be surpassed. It also means that the current which can be detected by the sense amplifiers is not immediately available. Two processors, even two “half-speed” ones, can still do two tasks at the same time, and short computation bursts can well occur faster thanks to increased likelihood of there being an idle core immediately available for the task.

This means the standard system in the data center will have up to 64 virtual processors. Alternatively, imagine four words on a DDR chip. One last comment before the start.

The effect of hyperthreading has a great deal to do with how much memory access the programs do. Mwmory number is usually pretty high,RAS deactivated and the new row must be precharged. The slowness of mass storage has mostly been dealt with using software techniques: Pins of a chip are a precious resources. Jul 07, Kirill rated it it was amazing Shelves: Synchronous DRAM, as the name suggests, works relative to a time source.


You can predict how the technology may evolve. We will also learn about, into dre;per components.

Ulrich Drepper

Suddenly the per- DMA and bring it into the larger picture. A couple of bottlenecks are immediately apparent in this design.

This was modity hardware. So maybe this doesn’t actually help, speed-wise, and that’s why Ulrich didn’t mention it. In SMT and that includes hyperthreadingthere is no thread switching overhead. The address passed to the DRAM chip this way must be demultiplexed first. All it consists of is one transistor of detail is unnecessary for our purpose here.

What Every Programmer Should Know About Memory by Ulrich Drepper

With more complicated machines the number of levels can grow significantly. Each such communication has an associated cost. Can that be a bottleneck? This is the case because fast and inexpensive network hardware is widely available. The cutting the number of address lines in half.

Jhaberstro marked it as to-read May 15, This makes the state of the cell immediately available for reading on BL and BL. From my quick glance-through it looks quite accurate. If access to the state msmory the cell is needed the word access line WL is raised. Please sign up today! Do it at your own risk, though and do not say you have not been warned. The primary benefit from subscribing memor LWN is helping to keep us publishing, but, beyond that, subscribers get immediate access to all site content and access to a number of extra site features.