The Bulldozer Aftermath: Delving Even Deeper
by Johan De Gelas on May 30, 2012 1:15 AM ESTInteger Crunching Power
Each core has two integer executions units (EX0 and EX1) and two AGUs (Address Generation Units). For comparison, the K10 core inside Magny-Cours and Istanbul had three ports to a “Fully featured ALU + AGU” couple. AMD marketing cleverly drew four pipeline blocks inside the Bulldozer integer core, but those powerpoint blocks cannot hide the fact that each Bulldozer integer core has fewer execution resources.
In practice, the AG0 and AG1 are little more than assistants with limited capabilities to EX0 and EX1.The software optimization guide for AMD family 15h processors lists only a few instructions (page 248 in the January 2012 version) that can be processed by the AG0 and AG1 execution units and each time the remark "First op to AG0 | AG1, Second to EX0 | EX1" is made. The AG0 and AG1 execution units reduce the latency of the CALL and LEA instructions, but the maximum throughput of each integer core inside the Bulldozer module is only two integer instructions per clock cycle. It's only when a fused branch enters EX0 and another integer instruction can enter EX1 that we have a slightly higher throughput of three integer instructions.
So the Bulldozer integer core can execute one integer instruction less per cycle (2 vs 3). That doesn’t mean that the Bulldozer integer core is 1/3 slower, however. The integer core of Bulldozer is smaller but also more flexible. The per lane dedicated 8-entry schedulers are gone, and a much larger 40 entry scheduler replaced it. This means that Bulldozer should be better at extracting ILP (Instruction Level Parallelism) out of code that has low IPC (Instructions Per Clock).
In some integer intensive applications, the fact that the maximum throughput of integer instructions is somewhat lower might slow things down. That is the not very useful "it depends" answer, so let's clarify: what kind of applications are we talking about?
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Homeles - Wednesday, May 30, 2012 - link
This. Read 3rd party reviews (like AnandTech!) -- several of them -- and draw your conclusions from there. That's pretty much the point of reviews; if marketing teams could provide honest, reliable benchmarks over a wide range of applications, we'd have little need for 3rd party reviews.Mugur - Thursday, May 31, 2012 - link
Well... they actually did!moravista - Wednesday, May 30, 2012 - link
Great article Johan! I have been reading your articles since the Pentium III / K6-2 days and have really enjoyed them! Thanks for sharing your insight! Keep 'em coming!JohanAnandtech - Friday, June 1, 2012 - link
Great to hear from you. Did you used to participate at the different forums on a different callsign?muy - Wednesday, May 30, 2012 - link
i want a phenom II x4 980+ on 32 nm. this whole idea of "lets put as many crippled dual cores on a die and smack a level 3 cache on top and call it out next cpu" is utter crap stuff that doesn't multi thread well (95 % of all stuff).6 core bulldozer i bought to replace my amd x3 450 is slower than the chip i wanted to replace at the same clock speed. now i have a shiny asus rog mb, a x3 450 powering it, and a 6 core bulldozer gathering dust. what a waste of money that was.
shame i can't find any x4 970+'s anymore and amd is to foolhardy to keep manufacturing their best gaming cpu's, let alone do a shrink on them to 32 nm.
i can only imagine how much better a phenom 2 x4 9xx, default clocked at 4.2 ghz+ would be than any bulldozer. (and how much cheaper to manufacture considering the die size compared to the die size of bulldozer).
i just don't understand amd.
Roland00Address - Wednesday, May 30, 2012 - link
Microcenter has these following processors1045t six core for $99
965 quad core black edition for $99
960t quad core black edition for $89 (this model is a disabled six core and has a possibility of unlocking to a 6 core. The 960t is a clearance processor so it is while supplies last.
fic2 - Thursday, May 31, 2012 - link
Those are all 45 nm. He is wanting a tick - a die shrunk Phenom II.Would have to agree with him. If AMD would do a die shrink they would have a killer product - assuming GloFo didn't f*ck it up.
muy - Wednesday, May 30, 2012 - link
bulldozer doesn't do single threaded, highly branching (cough games cough) stuff well.and before you say "some games use multiple cores", i'll say that 1 core running on 100 % and 7 cores at 5 % is not a good use of multi threading.
(1 * 100) + (7 * 5) = (1 * 100) + (1 * 35) - 1.35 cores used. this means that a DUAL core going at 10 % higher speed than the exampled 8 core would be 10 % faster than the 8 core 'using' it's 8 cores.
clock speed + ipc are the only things that matter 90% + of the time for games.
wolfman3k5 - Wednesday, May 30, 2012 - link
People don't buy CPUs based on theoretical performance, ideology or brand loyalty (OK, some fan-boys do). Most of us are not computer engineers, and even if we where, it wouldn't matter, because at the end of the day only the end result would matter: performance, efficiency and price. Just like I didn't buy Intel because it looked good on paper back in the glory days of AMD (cca. 2005). So no matter how deep and involved these articles are, AMD still trails Intel when it comes to performance, and it will do so until their lazy and incompetent CPU engineers will get off their lazy buts and start working. The sole reason why Bulldozer was such a massive fail was because most of the design process was highly automated. So, stop slacking and start working lazy AMD engineers!Homeles - Wednesday, May 30, 2012 - link
Being a "lazy" electrical engineer is practically impossible. The amount of work that has to go into making these processors simply function is quite massive. These guys work hard to get to where they are with their careers and work even harder to keep those careers. The margin of error here is also quite huge... a small flaw can create enormous performance penalties.I'd be willing to bet that many, if not most of Bulldozer's shortcomings could be blamed on management. Saying it was "lazy engineers" is callous and ignorant.