7 ms·

Normally I think readability is more important than speed. But in this particular case, I think GNU is doing the right thing optimizing the code to the limit.

• IshKebab 9y ago
  I totally disagree. Nobody will ever want to use `yes` at 10 GB/s. They will want it to be reliable, and this sort of over-optimisation increases the risk of bugs.
  • avar 9y ago
    I'm having a hard time imagining a case where even a grossly complex 100,000 line implementation of yes(1) couldn't be trivially proven to be correct.
    • fredmorcos 9y ago
      Absolutely, I once trivially proved a 1000,000 line implementation of return 0 to be correct. I don't know why all comments are bothered by how much overkill this yes implementation is. Maybe they don't hold 100,000 PhDs like we do, am I right?
    • acdha 9y ago
      I agree with the general point that you could prove such a simple program correct relatively easily but that does still have a cost, which is always a concern in an open-source project. You still need someone to step up and do that work and continue to verify it periodically in the future – if that code is doing complicated things with buffering, that opens up possible odd bugs due to stdlib, gcc, maybe even kernel behaviour changes which might not affect simpler programs. Not a huge bit of work to be sure but for a non-commercial project you might have trouble finding a volunteer who cares about that tedium.
    • mikeash 9y ago
      Easy! Write a program that does a brute force check of Goldbach's conjecture on all integers. For each integer that passes the check, print a line. If you can prove this correct (or incorrect) you'll probably win a Fields medal.
  • yk 9y ago
    The ability to get 10 GB/s dummy date into a pipe from the command line could come in handy at some point, for stress testing or something. I am not sure if it is over-optimized. (And even with the optimizations the risk of bugs should be very small.)
    • masklinn 9y ago
      Of course you could just pipe from /dev/zero which will easily do 10GB/s on every machine.
      • yk 9y ago
        Just tried it, cat /dev/zero|pv >/dev/null gives me roughly 2/3 the speed of yes. (5 GB/s vs 7 GB/s) Plus yes gives you an arbitrary string, instead of only zeroes.
        • tobik 9y ago
          That's because you're using cat and a pipe. Try this instead: pv > /dev/null < /dev/zero
          • mikeash 9y ago
            For anyone who is like me and finds it uncomfortable that things are now out of order, note that you can still put the input redirection in front: </dev/zero pv >/dev/null
            • vram22 9y ago
              Or even this: pv </dev/zero >/dev/null which is a common way of doing it (for any command with any inputs and outputs, not just the above ones), i.e.: command < input_source > output_dest All three pv command invocation variants, the one here and the two above, work. And it becomes more clear why they are the same, when you know that the redirections are done by the shell + kernel, and the command (such as pv) does not even know about it. So in all three cases, it does not see the redirections, because they are already done by the time the command starts running (with its stdin and stdout redirected to / from those respective sources). And that is precisely why the command works the same whether it is reading from the keyboard or a file or pipe, and whether it is writing to the screen or a file or pipe.
  • joosters 9y ago
    I've used 'yes' many times to generate huge amounts of data quickly. Back then, it never had the small string optimisation, but you could always run 'yes InsertReallyLongStringHere' to spew out data much faster than /dev/urandom or even /dev/zero I'm glad it runs fast, and I hope that all OS utilities are optimised (and tested, of course!) instead of making their source code pretty. The fact is, most people want to use programs, not read them.
    • masklinn 9y ago
      > you could always run 'yes InsertReallyLongStringHere' to spew out data much faster than /dev/zero That really doesn't make any sense, /dev/zero should be at least as fast as yes.
      • joosters 9y ago
        /dev/zero should be at least as fast as yes I agree, all I remember is that when I tried it, /dev/zero sometimes sucked performance-wise. I can't recall the exact circumstances as it was some time ago, and could have been on any of Linux/FreeBSD/SunOS/HP-UX/IRIX - perhaps it was the fastest common way at the time? On a recent x64 Linux, /dev/zero seems plenty fast enough now: $ dd bs=8k count=819200 if=/dev/zero of=/dev/null 819200+0 records in 819200+0 records out 6710886400 bytes (6.7 GB, 6.2 GiB) copied, 0.331137 s, 20.3 GB/s $ yes | dd bs=8k count=819200 of=/dev/null 819200+0 records in 819200+0 records out 6710886400 bytes (6.7 GB, 6.2 GiB) copied, 0.959551 s, 7.0 GB/s
        • Tepix 9y ago
          No need for "dd", let "pv" get the data from /dev/zero directly: $ pv < /dev/zero > /dev/null [ 16GiB/s] But the version of yes using vmsplice() is even faster than that on my machine.
          • pbhjpbhj 9y ago
            What's the line to test `yes` with `pv`? pv < /usr/bin/yes > /dev/null doesn't seem to work properly. FWIW I get 330MiB/s vs 8.4GiB/s for /dev/zero. [Incidentally first I've heard of pv but I've known about dd for a decade or two].
  • belorn 9y ago
    If you want to maximize readability and simplicity then writing `yes` in C is a bad choice. It is much easier, cleaner and shorter to write it in python or just use the shell which would normally be using the `yes` in the first place. Since `yes` is used in shells and builtins can be considered very reliable, here is a implementation as a shell function: yes(){ while :; do echo "${1:-y}"; done; } Python: import sys while True: if len(sys.argv) > 1: print(sys.argv[1]) else: print("y") And if you don't need the features of `yes` and only need a loop that prints 'y', then there really is hard to beat the simplicity of: while:; do echo "y"; done
    • raptorfactor 9y ago
      Is it really "easier, cleaner and shorter to write it in python"? Did you look at the OpenBSD implementation? https://github.com/openbsd/src/blob/master/usr.bin/yes/yes.c https://github.com/openbsd/src/blob/master/usr.bin/yes/yes.c It's essentially line for line identical to your python code...
      • fredmorcos 9y ago
        But it's C, and they're on HN, so C sucks, C should die, C is not modern, C is scary, C is bad, C makes them think, C forces them to be careful.
        • sctb 9y ago
          You've been on a tear of uncivil and unsubstantive commenting, and it has to stop. Often a good strategy for this is to slow down. High-quality reflective posts are what we're after instead of dismissive, snarky reflexive ones, and the former come more slowly.
      • belorn 9y ago
        The C example has three includes, two conditionals, two loops, and one function definition. The python example has a single include, conditional, and loop. For readability purpose it is easier to go through each lines of the python program than the OpenBSD C code. Its not massively different, but its distinguishable enough that I would choose the python version if I wanted to maximize readability, minimize syntax requirement and did not want to use shell script. The Shell function is in my view the superior choice if the audience is a programmer than know the shell script syntax. It is just a single loop and is written in the environment that the program is intended to be used in. The only drawback there is the speed.
  • th4dv 9y ago
    > Nobody will ever want to use `yes` at 10 GB/s Just because you say so?
    • bastawhiz 9y ago
      If the speed of yes is bounded by memory speed, doing anything useful will almost certainly consume that data at a far lower rate. Putting it on a disk, pushing it over a network, etc. will almost always be slower than yes is able to generate data.
      • cestith 9y ago
        The typical use case is piping it into another running program. Maybe someone wants to do that really quickly rather than putting it on disk or pushing it over a network.
  • MichaelBurge 9y ago
    'yes' to a file is how I sometimes benchmark disk speed. It should have fewer system calls than reading from /dev/zero and then writing. I actually checked just now, and it looks like you'd be making twice as many system calls with /dev/zero compared to generating the data locally: strace dd count=1 bs=512 if=/dev/zero of=test open("/dev/zero", O_RDONLY) = 3 dup2(3, 0) = 0 close(3) = 0 lseek(0, 0, SEEK_CUR) = 0 open("test2", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3 dup2(3, 1) = 1 close(3) = 0 read(0,"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 512) = 512 write(1, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 512) = 512 close(0) = 0 close(1) While 'strace yes > test2' is just a constant stream of write() calls. The difference matters if you're benchmarking e.g. some new SSD compared to a tmpfs on a machine with 100+ GB of RAM. It's always better if the tools have less overhead, because the comparison is more meaningful. Also consider that it can be faster to write to a local network than to disk. I've never done it, but I imagine that the kernel's not going to want to deal with your /dev/zero calls if it's spending all of its time writing to a 10GB switch. I can imagine some very specialized storage servers that could spend most of their time writing from memory buffers to a network switch, or if you're troubleshooting a slowdown in the networking itself.
    • wolfgang42 9y ago
      When I started this comment, I didn't think you were measuring what you thought you were measuring with those straces. 'strace yes > test2' only watches 'yes', not '> test2' (which is handled by the shell). Here's what your command outputs: $ strace yes > /tmp/test2 [various initialization steps] write(1, "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"..., 8192) = 8192 write(1, "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"..., 8192) = 8192 write(1, "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"..., 8192) = 8192 write(1, "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"..., 8192) = 8192 [...] To measure everything, I started up a whole new shell, expecting to see a 'write(1, ...)', a 'read(1)', and a 'write(f, ...)': $ strace -f sh -c 'yes > /tmp/test2' [various initialization steps] [pid 15839] write(1, "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"..., 8192) = 8192 [pid 15839] write(1, "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"..., 8192) = 8192 [pid 15839] write(1, "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"..., 8192) = 8192 [pid 15839] write(1, "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"..., 8192) = 8192 [...] How does this possibly work? File descriptor 1 is supposed to be the terminal, not a file! Of course, the magic of file redirection: open("/tmp/test2", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3 # Open the file, get FD 3 fcntl(1, F_DUPFD, 10) = 10 # Copy FD 1 (the terminal, STDOUT) to FD 10 temporarily close(1) = 0 # Close original FD 1 fcntl(10, F_SETFD, FD_CLOEXEC) = 0 # Close FD 10 (the terminal, copy of STDOUT) when exec() is called dup2(3, 1) = 1 # Copy FD 3 (the file) to FD 1 (STDOUT) close(3) = 0 # Close FD 3 (the file's original descrptor)
  • nobodyorother 9y ago
    Hey, 640K is enough for anyone!
  • peterwwillis 9y ago
    Unix userland tools have evolved over decades to be as efficient as possible because they have historically underpinned everything the operating system does. The faster each tool works, the faster the other tools that depend on them work. If increased efficiency results in a bug, that bug can then be fixed, making it a net gain for system stability.
  • tomohawk 9y ago
    It's not about running 'yes' at 10GB/s, it's about less overhead to do a simple job. If this version of yes is 100x faster, that implies it using 1% of a cpu to do the same work that would otherwise occupy 100% of a cpu. This leaves more of the machine to do what is likely to be the intended task.
• YSFEJ4SWJUVU6 9y ago
  It's not really optimized to the limit – or perhaps it is, but then the limit is fairly easy to reach. When I saw this item here I reached for the terminal and wrote a simple (and non-compliant) alternative that simply initialises 8150 bytes of "y\n" and then loops a write forever. I understand that it is not a fully standard-compliant yes, and that maybe GNU yes is indeed fast, but that awfully simple program that takes all of 10 lines (everything included) and took me all of a minute to write performs just as well as far as pv is concerned. (I eventually completed a feature complete yes but I still think that simply not using `puts` is hardly optimising to the limit.)