Memory Latency Impact on Performance
We just looked at the impact of memory bandwidth on performance, but what about latency? Let's first by adjusting the CAS latency from our default of 2 clocks up to 3 clocks. Almost all DDR400 these days is CAS 2 memory, but older memory may have a higher CAS latency or you may have to increase your CAS latency when overclocking to gain more memory bandwidth, so what kind of a performance hit is there when going from CAS 2 to CAS 3?
at_canals_08 |
at_coast_05 |
at_coast_12 |
at_prison_05 |
at_c17_12 |
|
Tcl = 2 |
116.12 |
140.43 |
123.37 |
113.69 |
83.15 |
Tcl = 3 |
115.52 |
137.07 |
121.91 |
113.37 |
79.92 |
At worst, CAS 2 memory seems to be about 5% faster than CAS 3 memory when looking at at_c17_12, our most CPU intensive test. While 5% alone isn't anything major, combine that with a number of other performance tweaks and they can definitely begin to add up.
Now let's look at keeping Tcl (CAS latency) fixed at 2 clocks, but vary Trcd timings from 3 up to 6 clocks:
at_canals_08 |
at_coast_05 |
at_coast_12 |
at_prison_05 |
at_c17_12 |
|
Trcd = 2 |
116.12 |
140.43 |
123.37 |
113.69 |
83.15 |
Trcd = 3 |
115.71 |
136.99 |
122.46 |
113.08 |
79.97 |
Trcd = 4 |
113.92 |
134.42 |
120.87 |
112.38 |
79.83 |
Trcd = 5 |
113.42 |
131.82 |
119.34 |
114.79 |
79.12 |
Trcd = 6 |
113.23 |
128.26 |
117.56 |
111.15 |
77.4 |
For the most part we saw no real changes when adjusting Trcd, the one exception being at_coast_05 which actually showed a pretty big difference between a Trcd value of 2 and higher latency values.
Next we'll look at adjusting Trp:
at_canals_08 |
at_coast_05 |
at_coast_12 |
at_prison_05 |
at_c17_12 |
|
Trp = 2 |
116.12 |
140.43 |
123.37 |
113.69 |
83.15 |
Trp = 3 |
115.6 |
139.24 |
123.13 |
116.35 |
82.09 |
Trp = 4 |
115.85 |
138.88 |
122.98 |
113.16 |
82.05 |
Trp = 5 |
114.84 |
138 |
122.65 |
112 |
80.98 |
Trp = 6 |
114.5 |
136.95 |
121.96 |
115.61 |
80.95 |
Here we see very little impact on performance.
Putting them all together we can see what the overall impact on using fast DDR400, higher latency DDR400 and extremely high latency DDR400 will be:
at_canals_08 |
at_coast_05 |
at_coast_12 |
at_prison_05 |
at_c17_12 |
|
2-2-2-10 |
116.12 |
140.43 |
123.37 |
113.69 |
83.15 |
3-3-3-10 |
114.47 |
134.11 |
120.64 |
112.62 |
80.56 |
3-6-6-10 |
110.74 |
123.76 |
114.75 |
112.17 |
73.8 |
Our standard 2-2-2-10 memory does actually offer reasonable performance benefits in Half Life 2 compared to DDR400 with higher timings such as 3-3-3-10 or the unrealistically high 3-6-6-10.
First and foremost Half Life 2 does appear to be rather dependent on memory bandwidth, but it is also quite appreciative of low latency memory as well. If you're wondering whether being able to run memory at low timings and high clock speeds is important, when it comes to Half Life 2 performance it is.
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Avalon - Wednesday, January 26, 2005 - link
Yep, I felt there should have been an Athlon XP in there, since many users are still running XPs, and many enthusiasts are running overclocked mobile bartons. I just assumed that an XP 3200+ would be equivalent to the 2.8ghz P4 they benched, and went from there.arfan - Wednesday, January 26, 2005 - link
I think Half Life 2 is more friendly than DOOM3. We can play HL2 with old video card (entry level video card). But to play DOO3 we need mid range video card :(blckgrffn - Wednesday, January 26, 2005 - link
Agreed, there are a lot of us that are still running our XPs. Hard to beat the bang for the buck on that platform, but just how much are we missing out?Jeff7181 - Wednesday, January 26, 2005 - link
Awesome article. Only thing I would have liked to see is an Athlon XP3200 (as outdated as it is) in the mix as well just to see where it would fall on the charts.acejj26 - Wednesday, January 26, 2005 - link
Good to see Anand writing articles again. I get tired of seeing grammatical and spelling errors in articles written by some of the other guys here. Anand's articles are always well thought and just seem more professional. Good job. I also appreciated the Mac Mini article yesterday. Keep it up.Dranzerk - Wednesday, January 26, 2005 - link
Good article, came out in the right time I was considering upgrading my ATI 9700 Pro/2.4ghz P4 to a athlon 64 or a 6600GT. Guess its the Nvidia 6600GT :DThe only thing holding me back (others to) is the AGP vs PCIx deal, but with NF4 chipset with AGP it should be a no brainer now to just stick with old AGP card and have lot of life in it for time to come.
George Powell - Wednesday, January 26, 2005 - link
Awesome article. Made for a really good morning read.morcegovermelho - Wednesday, January 26, 2005 - link
There is an error on page 2. The value for athlon 3500+ at_coast_12 is 11.58.
Great article