clamchowder

vor 11 Monatendiscuss

(author here) they try for all instructions, just that it's a prediction w/replay because inevitably some instructions like memory loads are variable latency. It's not like Nvidia where fixed latency instructions are statically scheduled, then memory loads/other variable latency stuff is handled dynamically via scoreboarding.

clamchowder

letztes Jahrdiscuss

It does clock ramp from 800 MHz idle to 3.2 GHz under load, with 900, 1000, 1100, 1300, 1500, 1800, 2200, and 2700 MHz steps in between until it hits 3.2 GHz after 71.6 ms. Article was getting long enough so I just left it at, it reaches 3.2 GHz and stays there even though the spec sheet says it should go higher.

I remoted into the system for testing (Cheese/George had it), and he said it took 3-4 cold reboots for it to come up, and suspected memory wasn't training correctly. So I did all the testing without ever rebooting the system, because it might not come back up if I tried.

clamchowder

letztes Jahrdiscuss

It was a joke about blurriness. To extend the joke, be glad it doesn't flicker and shimmer.

But yes, platforms usually apply compression in terrible ways, and it's especially noticeable coming from text and straight line stuff like graphs

clamchowder

letztes Jahrdiscuss

Yea Wordpress was a terrible platform and Substack is also a terrible platform. I don't know why every platform wants to take a simple uploaded PNG and apply TAA to it. And don't get me started on how Substack has no native table support, when HTML had it since prehistoric times.

If I had more time I'd roll my own site with basic HTML/CSS. It's not even hard, just time consuming.

clamchowder

letztes Jahrdiscuss

(author here) When I checked the 7600 XT was much more expensive. Right now it's still $360 on eBay, vs the B580's $250 MSRP, though yeah I guess it's hard to find the B580 in stock

clamchowder

letztes Jahrdiscuss

Oh that should be fun. Would have to fit it around work though

clamchowder

letztes Jahrdiscuss

"don't run any faster than a sequence of simpler instructions"

This is false. You can find examples of both x86-64 and aarch64 CPUs that handle indexed addressing with no extra latency penalty. For example AMD's Athlon to 10H family has 3 cycle load-to-use latency even with indexed addressing. I can't remember off the top of my head which aarch64 cores do it, but I've definitely come across some.

For the x86-64/aarch64 cores that do take additional latency, it's often just one cycle for indexed loads. To do indexed addressing with "simple" instructions, you'd need at a shift and dependent add. That's two extra cycles of latency.

clamchowder

letztes Jahrdiscuss

No, that's not a second level BTB in that regular direct branches don't seem to use it. It's only for predicting indirect branches.

clamchowder

letztes Jahrdiscuss

(author here) Just a 32 entry BTB is technically a possibility from microbenchmark results, but the EIC7700X datasheet straight up says:

"a branch prediction unit that is composed of a 32-entry Branch Target Buffer (BTB), a 9.1 KiB-entry Branch History Table (BHT), a 16-entry Return Address Stack (RAS), 512-entry Indirect Jump Target Predictor (IJTP), and a 16-entry Return Instruction Predictor"

clamchowder

letztes Jahrdiscuss

(author here) I compared it to the A75 on the Snapdragon 670, not the 845. I chose that comparison because I have a Pixel 3a (my previous daily driver cell phone), and that's the only A75 core I had access to.

clamchowder

letztes Jahrdiscuss

(author here) by free time and curiosity I mean, I have a day job so I'm able to do this as my hobby

clamchowder

vor 2 Jahrendiscuss

Note - I saw the article through from start to finish. For power measurements I modified my memory bandwidth test to read AMD's core energy status MSR, and modified the instruction bandwidth testing part to create a loop within the test array. (https://github.com/clamchowder/Microbenchmarks/commit/6942ab...)

Remember most of the technical analysis on Chips and Cheese is a one person effort, and I simply don't have infinite free time or equipment to dig deeper into power. That's why I wrote "Perhaps some more mainstream tech outlets will figure out AMD disabled the loop buffer at some point, and do testing that I personally lack the time and resources to carry out."

clamchowder

vor 2 Jahrendiscuss

Yes, I tested on CCD1 (the non-vcache CCD) on both BIOS versions.

clamchowder

vor 2 Jahrendiscuss

Seems like no one ever reads the byline anymore

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