This reminds me of a story from 15 years ago, where I was developing a technology to download games on demand by hooking into the OS calls.
There was a particular game that was superslow when this tech was applied. Original game loading took around 15-20 seconds, whereas once the tech was applied it took easily 3-5 min, even with all data already downloaded.
When I started digging into it, I realized the reason was the game was using something like
fread(data, 1, 65536, fptr);
fread(data, 65536, 1, fptr);
The easy fix was to swap arguments for certain calls. The long fix required to use an internal cache to account for these cases so that the hooked ReadFile was faster when data was already in disk.
Funny thing is that as we started rolling out the tech and applying it to more and more games we realized lots of games did this. We went for the cache fix and games ended up loading faster than before. Honestly, games could have load all the data in a couple of seconds by just swapping the args. I'm guessing developers did this on purpose so that games seemed like they were loading a lot of stuff, although you never know.
I used to be a graphics card/chip architect for macs in the early/mid 90s - our chips were the fastest, but some programs were resistant because they did stupid stuff: pagemaker invalidated the font cache every time it went thru its main loop, quark with ATM did an n*2 thing every time it wrote text etc etc. We had special hardware to accelerate text drawing and it did nothing because the software pissed it away. We considered creating a plugin that fixed all these things, it would have been hard to maintain, in the end we travelled around to the people who made these apps and talked them through their problems
To be fair excel would erase places white that it wanted to write up to 9 times before it drew any black pixels, we made that very fast! we didn't tell them :-)
At the time 24-bit framebuffers were so slow that before we built graphics acceleration hardware people would switch back to 8-bit to get stuff done, making 24-bit/true colour your daily driver was a big step forward.
Does that make you the first in a long tradition of GPU developers going to blockbuster app devs to say "hey, you should be doing this instead?"
PS – I am looking through the NuBus cards that I have... did you work for SuperMac or RasterOps?
I was probably not the first to have to do that, we knew what apps our customers used, making them better was the whole point of the operation
I did the architectural design for the SuperMac cards. I figured out what needed to be accelerated, dropping code into people's machines to see where the cycles were going. Others did the physical design for the first 2 cards, I did the design of the chip in the Thunder and later cards (designed the data paths and state machines and a full simulation, someone else actually laid the gates)
If your card has a SQD01 on it it's my work. It peaks at 1.5Gb/s on solid fills
This is a horrible and yet not unexpected insight into the internals of Excel
To be fair this was Excell 25 years ago, may no longer be true.
One of the other bugs (the Quark/ATM one) was also because of the programmers were worried about writing over stuff that hadn't been completely erased, the Quark guys wrote a string with 2 spaces at the end through a box that masked the end of the string, the ATM font renderer saw it couldn't fit the text so it split it in half and tried again so it drew N/2 N/4 N/8 ... strings. It spent all it's time in the 68k's multiply instructions figuring out how wide the strings (and substrings) were, our fancy 24-bit character rendering hardware was an afterthought
There's a good chance it was Excel's workaround for some other GPU's buggy behavior.
In all of the software you’ve written, are you aware of how many on-screen pixels you’ve overdrawn?
> To be fair excel would erase places white that it wanted to write up to 9 times before it drew any black pixels
I feel like I'm having a stroke trying to read this, what does it mean??
Well all they needed to do was erase the screen with white and draw on it, but their app's internal logic meant that they erased it more than once.
I was capturing QuickDraw library calls - the low level graphics primitives, to figure out where the graphics time in apps was going and found out sometimes excel did it 9 times
Of course users didn't see it more than once, but our hardware made all that wasted time run faster
It's more likely that one dev wrote the draw-cell code.
Another dev who's fixing a bug, realizes if they call a certain function either directly or indirectly, their particular bug gets fixed.
Oh, and as a side effect, the cell gets erased (again).
A few more fixes/new features added like this and the code is inadvertently erasing the same cell multiple times.
It takes a certain type of dev to step through in a debugger and Notice the app is doing way too much work and then to untangle the mess of code without causing regressions.
Maybe their CRTs had horrible burn-in and they had to erase everything 9 times before it was gone...
Several layers of white is what makes the black really pop. (Just kidding).
It’s necessary for erasing cat pixels.
I think it could call (their equivalent of) clearRect up to 9 times on an already cleared region before drawing there?
It means they were time travellers! Secretly, they came from an alternate future where everyone used e-ink displays, and wanted Excel to be ready!
before writing to some area, it would erase it (clearing with white) up to 9 times
I remember when 24 bit color was exotic and aspirational and you had to settle for 16.
Yeah, even in Linux we were doing these things with X Windows bit depths.
8 bit psuedo color, so the color palette switched with every focus-follows-mouse window boundary crossing. 16 bit direct color with banding but no more palette psychedlia.
This was equal parts to make it faster and to allow for higher framebuffer resolutions with limited VRAM.
I got the extra vram in my LC to allow for 24-bit color but it was dog slow. The 16 bit data path didn't help. If I wanted it, I'd get things done in 8 bit or mono until it was ready, then switch to 24 bit for the final look.
I swear if Sun Microsystems was still around, their machines would still ship with 8-bit pseudocolor and you'd have to pay an extra $3k for 24-bit.
16 bits? Luxury. I had 6 colors when I was a kid and was happy to have them.
My first computer was a TRS-80 Color Computer which had a tiny set of badly chosen colors!
Back then you did what you could with graphics and it wasn't a lot. After I got a PC I had indexed color for a long time and working with indexed color was pretty rough because anything physics-based like rendering or raytracing was going to be difficult. You could render a photo pretty well with 256 carefully chosen colors and dithering but if you wanted to, say, composite two photos and do general sorts of things you'd need to convert to "true color", do the math there, then re-quantize for display.
6?!? We had only 4 colors in low res mode and 2 in high res
Well my Hercules graphics card was only monochrome, but it was relatively high resolution.
I had a herc clone on the 286 machine I bought around 1987 and later added a Super VGA card. One cool thing about the IBM PC was that the monochrome and color graphic systems were sufficiently different in terms of memory map and ports so you could plug in two graphics cards and two monitors and that's what I had.
What would have been the purpose of stupid code like that?
Was it a workaround for things that didn’t fully complete on one iteration, so the devs kept hammering away at it until it worked?
They were most likely just bugs. Quite possibly really stupid bugs.
Not every bug results in the program doing the wrong thing, they often just make the program do the right thing very slowly.
And nobody notices, since it still produces the right result.
Yes, they were bugs, I think programmers (and their marketing people) were more focused on new features than performance
Thankfully we’ve moved past that era.
Now the bugs that get ignored for new features cause bad results AND bad performance.
It's not necessarily stupid code in the game, but something the C library is doing that it probably shouldn't.
If the stream is buffered, then all operations, including fread, are supposed to go through the buffer.
All three of these should issue buffer-sized reads to the operating system:
1. A loop which calls getc(stream) 65536 times.
2. fread(buf, 1, 65536, stream)
3. fread(buf, 65536, 1, stream)
The more direct behavior of fread should only kick in if the stream is configured as unbuffered.
I would say that the way low-level reads are issued to the host operating system is a "visible effect" of the program, so I suspect this may actually be a matter of conformance. I.e. it's not okay to issue those reads however the stream library wants as long as the data is read.
Reminds me of the "community patch" to GTA Online from a few years ago. The game was plagued by 10+ minute loading times. The situation remained for years and only got worse with time. Some hacker figured out that the game spent 80% of loading time reading the in-game store listing file. The file was tens of megabytes IIRC, and it literally used the Schlemiel the Painter's Algorithm - for each entry, start reading from the beginning byte after byte. The hacker made a tiny patch that made it remember where it found the last entry. This cut the total loading time by 80%, from over 10 minutes to less than 3.
Edit: removed incorrect information.
This is not quite an accurate telling of rockstar's reaction, there were actually receptive to it and paid out $10k for the discovery. Though it's an understandable mistake given rockstar's hostile history with the gta modding scene.
See the original post and discussion for the whole story:
https://nee.lv/2021/02/28/How-I-cut-GTA-Online-loading-times... https://news.ycombinator.com/item?id=26296339
That's not how I remember these events when they were playing out. I distincly remember social media posts warning about the dangers of modifying game files, plus refusal to acknowledge the issue. Note there were 2 full weeks between the blog post and the update mentioning the bounty. I'm pretty sure the massive community outrage in between has played a role in it. But I don't have any sources and I was wrong about at least one thing (lack of attribution), so I'm okay assuming I'm wrong about everything else too.
Wowee two full weeks? You mean like a single sprint to discover, verify, and post PR about a perf patch that was good among the sea of rumors and reports a billion dollar game usually gets?
I mean like enough time to check the pulse with the community and walk back the initial confrontational response. I don't have a problem with when they fixed it. I don't have a problem with when they paid out. I wouldn't have a problem if they didn't pay out at all (why would they?). I have a problem with their initial reaction, which was full of the usual fearmongering against modders. (And a smaller problem with that it took an external contributor to finally make them implement a trivial fix for a massive usability issue that's been there for at least 6 years. It shows how much they don't care about their customers or the product they're selling unless the media get involved.)
> Which basically expanded back in the day to 65k reads of 1 byte for several MB file. Each fread translated to 65k reads of ReadFile Windows API
What software did that that badly? If the code asks for (up to) 65,536 single byte items, why would you split that into 65,536 calls?
Also, that change changes behavior. The old call could read anything from zero to 65,536 bytes, the new one only can read zero or 65,536 bytes.
(Reading the source of a few implementations, I think most implementations will fill the output buffer with partial objects if the input doesn’t supply an integral number of them, but the return value of fread cannot signal that to the caller)
The standard says that fread calls fgetc multiple times for each object:
> For each object, size calls are made to the fgetc function and the results stored, in the order read, in an array of unsigned char exactly overlaying the object
(wording unchanged since C99)
If the file is unbuffered, depending on how the implementation handles buffering, and how it interprets the standard, then perhaps it does end up hitting a path where there's 1 ReadFile call per byte...
I don't know how most implementations get around this. Presumably it's valid to interpret "calls are made" as "behaving as if calls are made", meaning fread can copy data out of the FILE's buffer directly, or make calls directly to whatever routine fgetc defers to, rather than calling fgetc N times literally. Looks like glibc's fread does this.
I think it’s pretty rare for files to be unbuffered like that. AFAIK it’s mostly stderr that ends up unbuffered, at least on Unix-like systems.
You can call setbuf(fp,NULL) after opening, and now the stream is unbuffered. What this means is apparently implementation-dependent.
As to why you'd do that? - well, who knows the exact circumstances in this case. Perhaps this was faster in some meaningful case that was relevant to some other project (and then maybe the fread doesn't call fgetc after all!). I'm just speculating. Well-reused code often ends up with stuff that needs rethinking, that, even if noticed, nobody has the time or inclination to attempt to fix.
A long time ago I worked with someone who read 1 byte at a time from a socket because they insisted data was cached so the kernel was going to batch it magically somehow. It took me days to convince them to measure it.
I used to make it a general rule to start all my optimisation of any network code by running strace and look for excessive read's and write's, because you'd be shocked how many did stuff like that if they didn't know the length of a string, or to read the length first, instead of reading into a buffer.
I had to convince people with benchmarks regularly that, yes, you could write the handful of lines to do proper user-space buffering and trivially run rings around any code that did extra context switches, because a lot of people didn't realise the cost difference between system calls and calling their own functions.
This included, by the way, the MySQL client library, at one point, which would do small read for length fields instead of larger non-blocking reads into a buffer all the time
That's different: you're talking about the application code, like OP.
But I think the parent comment's point is that the issue is in the implementation of fread itself in the standard library. It's perfectly reasonable for an application to pass it 1, 65536 (i.e. one byte, up to 65536 times) and expect it not to issue 65536 separate OS calls.
Is it? I get what you're saying, but asking for 1 byte 65536 times, is indeed different than asking for 65536 bytes, 1 time. There may be reasons, such as when you pull off the end of a buffer, it shifts. And the buffer size is 1 byte. Or 10. Or whatever.
No, I'm not saying that's why. I'm simply saying there is a difference between asking for 1 byte or 65k bytes of something. Even dd runs the same under Linux.
dd bs=10k count=1 is faster than bs=1 count=10k
I remember trying to recover some data from a spinning disk, and trying to slowly creep up on the data. So I wanted 1 byte per, I wanted it to nibble, until it hit whatever the errored part was. If I just grabbed the lot, it'd error out from the whole read.
I glanced at https://github.com/busterb/libc-openbsd/blob/master/stdio/fr... and https://chromium.googlesource.com/chromiumos/third_party/gli....
The latter (as usual when comparing OpenBSD and Linux) is more complex, but both multiply count by size and then go their way.
Also, the API contract allows fread to read fewer bytes than requested. I would except any implementation to do that.
But maybe, somebody interpreted the contract differently than major OSes, in the sense that a call isn’t allowed to write partial size-sized chunks to user memory and/or advance the file position further than its return value advocates (that, I think, is something that the implementations above can do, and might be considered a bug)
> asking for 1 byte 65536 times, is indeed different than asking for 65536 bytes, 1 time.
Yes it's different. As others have noted, the difference is what is returned if less than 65536 are available to read in the file: total failure vs partial read.
There is, unsurprisingly, no requirement that it has an unnecessarily inefficient implementation to meet this behavioral requirement. (The C standard doesn't talk about such things as syscalls but, even if it did, it surely wouldn't require such a thing.)
The irony is that that partial read is actually the default on both Windows and Posix (i.e. both ReadFile and read() will read up to the number of bytes specified). So a one-syscall implementation for fread would have been easier than multiple calls, and certainly would be standard compliant.
The dd example isn't comparable because dd is much lower level, and you really are specifying how the syscalls should be made.
Also you need to be careful what you read/write. In some cases.
As many examples out there use int/char etc to show how to use the thing. But if you switch to structs that fwrite can totally burn you if you use the sizeof call. As the sizeof a struct can vary between platforms and compilers. Depending on packing. Then endianness can sometimes mess you up. If you are reading/writing for yourself you can get away with a lot. But if you are trying to interop then you have to be wildly careful what you do.
fwrite is another one where people will do one byte at a time (same up to for the windows version). Bash out a loop, use the sizeof for the input to the for loop. copy and paste just doing 1 byte and you can easily end up here. One program I added a cache in front of the thing so it would always write on disk block boundaries and then come back for more. I started off with just packed struct sizes but the perf was just 'ok'. The file block boundary thing really made it fast. Not all OS's have a readahead/write buffer behind that call so perf can vary.
It is honestly such an easy mistake to make. As many of the examples/docs do not really show you why/how to use both of those calls in the way needed. You sort of have to stumble into it and work it out.
Once you see it you know. But until then you do not really notice if it is 'working'.
Another possibility for why it needs to be done that way is dealing with error conditions.
I've not looked at the code (or even the man pages) and it is a long time since I touched anything that low level, so this might be completely wrong, but if there is an error before the next 64KiB (including just hitting EOF) then the semantics could be different. Asking for 1x64KiB I would expect to just error as there aren't the requested number of bytes. Asking for 64Ki lots of 1 byte might simple error just the same, or it might at least populate the buffer with what it can read, or if the meaning of 1,65536 is actually “up to 64Ki lots of 1B” then it would populate the buffer as far as possible and return the amount read rather than an error condition.
If the per-byte option is slow but still fast enough, and dealing with the semantics is less faf, then people will go for that because the tiny time loss is worth the larger effort reduction. Of course this assumes the underlying system doesn't change, as with the “making local code to run as on-demand networked code” example higher in the thread which changes the relative performance characteristics of the two calling methods significantly.
dd is designed to request a certain block size from the kernel. fread is not and should just multiply the two arguments and read that many bytes, just like calloc.
I assumed it was a simple mistake: easy to forget what order the two integers are sent.
Wait, is that wrong? I always call fread as:
with the rationale that I'm interested in reading sizeof(buffer) individual bytes. The buffer size is incidental, not the size of the items I'm trying to read from the file; "read one item whose size is sizeof(buffer)" seems semantically wrong.Is this just the case of Windows having a bad stdlib fread implementation 15 years ago or is my thinking here actually wrong?
It's not wrong. Guy just wrote a bad implementation of fread and blamed everyone else.
He didn't write it.
The C runtime authors did (presumably Microsoft, if it's MSVCRT).
He's hooking into ReadFile, a layer below the stdlib. By the time it reaches the hook, it's already split.
fread should be buffered, but different values may cause buffering at different rates. Perhaps it didn't generate 65535 calls to ReadFile but it generated 16 or 64.
Part of Windows Explorer actually does tons of tiny 4 byte ReadFile calls in to its tracking database like file when you delete a file. If you deleting lots of files this quickly adds up.
Is this why Windows takes so long to delete things?? Presumably those reads aren't done when using del from a console as that always seems a bit faster.
Its slowness is also a function of security software or any other file system "filters" (I believe they're called) are installed.
For example, I run TortoiseGit which has a caching feature which is supposed to make it faster at showing what to commit. Disabling it increases the number of items I can delete per second in my Windows Explorer from about 1000 to about 3000 while making not making TortoiseGit operations meaningfully slower (that I can tell).
This is a Dev Drive [0] on my machine, it would probably be slower on my C: drive which has full Windows Defender real time file scanning.
[0]: https://learn.microsoft.com/windows/dev-drive/
Windows Explorers zip implementation also seams to do 1 byte reads by the speed is has compared to every other zip implementation.
It is frustrating how slow .zip (and more recently .7z) support built into Windows Explorer is.
This is a great article on why it's so unreasonably slow to modify these archives: https://textslashplain.com/2021/06/02/leaky-abstractions/
But it doesn't seem to explain why it's so much slower at regular extraction.
> The long fix required to use an internal cache to account for these cases
That's because the OS does the same thing too. It's the right fix, when I implemented something similar, we implemented caching right away.
Doesn't that break anything relying on the return value? fread gives you the number of objects read as a return. So I think a pretty typical thing would be to fread and then parse that number of characters, and that'd just break?
I've seen a lot of code that just assumes fread / fwrite succeeded without bothering to check the return value...
But in this case if the code was calling fread 65536 times in a loop and getting 64KiB each time it wouldn't be good either!
Sounds like the parent comment had to fix this with the internal cache thing to speed up the small freads. I think they meant the easy fix would have been swapping the args in the original / caller code.
There are no small freads in the story, whatever implements those freads supposedly split them up into many calls. But that sound more like a problem of that implementation than the fread callers as size == 1 is correct when you are reading a bag of bytes.
I think they turned it from a tiny file read to a tiny ram read.
The type of programmer who swaps the args to fread tends to be the type of programmer who doesn't bother to check the return value, fortunately.
Edit: mort96: So did you check the return value or not?
If I have a buffer of bytes, and I intend to treat the content of that buffer as individual bytes, what is semantically wrong with "read 65k 1-byte-sized items into this buffer"? Wouldn't it be a bit unnatural to express it as "read one item whose size is 65k"?
But the args aren't necessarily swapped just because they end up in a slow case in some implementation.
"I'm guessing developers did this on purpose so that games seemed like they were loading a lot of stuff"
I really hope that was not the case and rather think incompetence or to deal with obscure legacy problems, but the gamer in me gets enraged at the thought someone would artificially increase loading times.
The most important fix in SP1 for Office 2007 was fixing exactly that in Excel. Doing ridiculous amount of 4 byte reads made it basically unusable on network filesystems.
Why does your fread to anything other than multiplying the two arguments?
The idea of having two arguments to fread() is presumably to be able to do something else than all-or-nothing when there's a short read.
Yes, it divides the bytes read by the element size to get the return value.
Which is the obvious reason you'd pass an element size of 1: you want to know how many bytes were read.