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| -rwxr-xr-x | .times | 14 | ||||
| -rw-r--r-- | served/words/statistics-on-linux.html | 197 |
2 files changed, 204 insertions, 7 deletions
diff --git a/.times b/.times index 7986788..4351af0 100755 --- a/.times +++ b/.times @@ -1,7 +1,7 @@ ,1722699430,1739445155,1739445155 .DS_Store,1716265453,1739645865,1739646135 .times-ignore,1708577778,1708577778,1724111977 -.times,1714751011,1740909645,1740909580 +.times,1714751011,1740909668,1740909660 readme.md,1739445155,1739445155,1739445155 .gitignore,1739445155,1739445155,1739445157 updateTimes.sh,1708577778,1708577778,1740776196 @@ -18,7 +18,7 @@ templates/post.html,1739445155,1739445155,1739445200 templates/base.html,1714750761,1733662976,1733662976 templates/minimal.html,1708593919,1708593919,1724111977 served,1722699430,1740573462,1740573463 -served/home.html,1739445155,1740909265,1740909265 +served/home.html,1739445155,1740909265,1740909645 served/.DS_Store,1716265453,1739645865,1739646135 served/about.html,1740572535,1740573730,1740573730 served/look1_512px.png,1734785632,1734785632,1734895881 @@ -27,14 +27,14 @@ served/starlight.html,1739700272,1740909559,1740909577 served/gennysomething.gif,1740573462,1740573462,1740738464 served/atom.xml,1721484969,1736549409,1736549409 served/look1_512px_squash.gif,1734785650,1734785650,1734895881 -served/words,1722699427,1740534158,1740534159 +served/words,1722699427,1740909658,1740909660 served/words/debugging-my-sql-query.html,1739445155,1739445155,1739445200 served/words/a-really-long-week.html,1731536606,1734517744,1734517744 served/words/.DS_Store,1731546328,1739645858,1739646135 served/words/words.html,1739445155,1739445155,1739445156 served/words/akkoma-postgres-migration.html,1712999241,1712999241,1724111977 -served/words/statistic-gifs.html,1740534158,1740909628,1740909628 -served/words/writing.css,1739445155,1740907336,1740907337 +served/words/statistics-on-linux.html,1740534158,1740909628,1740909645 +served/words/writing.css,1739445155,1740907336,1740909645 served/words/words.css,1739445155,1739445155,1739445156 served/words/seeding-rng-physically.html,1739445155,1739445155,1739445156 served/words/images,1731545028,1735837530,1735837532 @@ -87,11 +87,11 @@ served/cohost/gif-selfies/pngd_nv12_3.webp,1707511212,1707511212,1724112458 served/cohost/gif-selfies/yay_color.gif,1707511212,1707511212,1724135237 served/cohost/gif-selfies/pngd_nv12_2.webp,1707511212,1707511212,1724112458 served/styles,1722699427,1740573422,1740573426 -served/styles/home.css,1739445155,1740909209,1740909211 +served/styles/home.css,1739445155,1740909209,1740909645 served/styles/Recursive.woff2,1656619120,1656619120,1733663978 served/styles/Atkinson-Hyperlegible-Bold-102a.woff2,1589485906,1589485906,1733665201 served/styles/post.css,1739445155,1739445155,1739445156 -served/styles/common.css,1739445155,1740826395,1740826397 +served/styles/common.css,1739445155,1740826395,1740909645 served/styles/about.css,1740573416,1740573835,1740573863 served/styles/writing.css,1724117827,1731504611,1733662439 served/styles/Atkinson-Hyperlegible-Italic-102a.woff2,1589485906,1589485906,1734781985 diff --git a/served/words/statistics-on-linux.html b/served/words/statistics-on-linux.html new file mode 100644 index 0000000..583974b --- /dev/null +++ b/served/words/statistics-on-linux.html @@ -0,0 +1,197 @@ +--- +template=post +title=Statistics on Linux with /proc +style=/styles/post.css +style=writing.css + +published=2025-03-02 4:00am CST + +description=I want to tell you how my statistic gifs are made :) +--- + +<style> + .manlink { + margin-top: -1rem; + } +</style> + +I've been wanting to make a little page for the statistics of my +webserver <i>(the system not the program)</i>. When I started to +research the APIs that I'd need, just on a whim one day with no +intention to start, I got grabbed by it and knew I had to start. + +Check it out: <a href="/starlight.html">starlight.html</a> + +<h2>a <code>/proc</code> foreword</h2> +The <code>/proc</code> filesystem, on Linux, is a sort of window into +the kernel. It lets you view some pretty detailed information by simply +reading some files (thanks everything-is-a-file linux). + +There's a lot of information about it in the man pages. +They might all be in one big one at <code>man proc</code> but, +like how they are on my server, they could be broken into separate pages +for distinct sections. + +I have linked the relevant pages at the top of their section. It's a link +to man7.org, which seems to be <i>the</i> source for Linux Kernel man pages +on the internet. man7 is linked from kernel.org which lends it +credibility at least. + +<h2>Memory</h2> + +<p class="manlink"><a href="https://man7.org/linux/man-pages/man5/proc_meminfo.5.html">man7.org/proc_meminfo</a></p> + +This one isn't too hard. I open the file <code>/proc/meminfo</code> and +look for the lines starting with <code>MemTotal</code> and <code>MemAvailable</code> +which are the total memory and currently available memory, respectively. They +are very well named :). For usage, I just subtract available from total. + +<h2>Network</h2> + +<p class="manlink"><a href="https://man7.org/linux/man-pages/man5/proc_net.5.html">man7.org/proc_net</a></p> + +If you <code>cat /proc/net/dev</code> you can see some stats about +your networking interfaces. This is what I parse, with some pain. + +I read the bytes columns from the receive and transmit sections. +These are total counts of bytes received since boot, so you'll +have to take two samples and subtract to get the number of bytes +in some time-span. + +Looking at it in the terminal, you might assume that the separator +between the columns was a tab character. I sure did! It is not a tab, +but many spaces. + +Because of spaces-and-not-tabs +<i>(not the tabs vs. spaces debate of usual, but with similarities)</i>, it proved +to be a bit annoying to parse. It made me finally +pull in a regex crate because I didn't feel like dealing with it +at the time. Eventually™ I want to write a skip-arbitrarily-many-whitespace +iterator, but for now <code>regex-lite</code> lives in my <code>Cargo.toml</code>. + +<h2>CPU</h2> + +<p class="manlink"><a href="https://man7.org/linux/man-pages/man5/proc_stat.5.html">man7.org/proc_stat</a></p> + +<code>/proc/stat</code> is the least obvious of the triplet. It has more than +just the CPU's information, but the cpu is what we're after. You'll notice many +CPU lines probably! I'm using the one starting just "cpu" without a number +(cpu0, cpu1, etc.) because I only have the 1 core. If I had more than one core +it'd work similarly, the just-cpu line sums the other ones, but then it could +show >100% usage 'cause it's per-core usage just added together. + +First things uh, second? To summarize from the man page:<br /> +The units of these values are <i>ticks</i>. There are <code>USER_HZ</code> +ticks per second. On most platforms it's 100 but you can +check the value for your system with <code>sysconf(_SC_CLK_TCK)</code>. + +<details> + <summary style="font-style: italic;">small C program to check _SC_CLK_TCK :)</summary> + <pre><code>#include <stdio.h> +#include <unistd.h> +int main() { + printf("USER_HZ is %i", sysconf(_SC_CLK_TCK)); +}</code></pre> +</details> + +But what columns of data do we use? From <a href="https://stackoverflow.com/a/3017438">this stackoverflow answer</a> +it seems that summing the user, nice, and system columns get you the total ticks. +The user and system make sense to me, time spent in user and system mode, +but what on earth is nice? I sure hope it is. + +The Internet tells me to check <code>man nice</code> +(<a href="https://man7.org/linux/man-pages/man1/nice.1.html">man7.org/nice</a>). +That page says that the +nicness of a process can be adjusted to change how the kernel schedules +that process. Making it less nice (down to -20) increases it's priority, and +increasing it's niceness (up to 19) lowers it. I guess that makes sense. Lowering +the niceness makes the process greedier and in want of more attention +from the scheduler? I'm unsure how well that personification tracks to reality, but +it helped me think about it. + +The nice column, then, seems to be the time spent in processes that +would go in the user column, but they have a different priority and +I guess differentiating that is important. + +Oh, but there might be more columns we want! +There's <a href="https://stackoverflow.com/a/10794088">another S.O. answer</a> +that I found while writing this that says the sixth and seventh columns should used +as well. These are irq/softirq and are time spent servicing +interrupts. I think it makes sense we'd want that, too. + +So you have all these columns—user, nice, system, irq, +and softirq—that add together to give you the total number +of ticks spent Doing Things since boot, and you have the number +of ticks in a second. Can you see where I'm going with this? + +Yup, take two samples some time span apart, subtract the former +from the later, and then you have how much time the processor spent +Doing Things. You can use that and the number of ticks in your time +span to calculate utilization. Or you just have how much actual time +The Computer spent Doing Work which is also pretty neat. Maybe you +can pay it an hourly wage. Is that just AWS? + +Something to watch out for:<br /> +apparently the numbers in <code>/proc/stat</code> can overflow and +wrap back to zero. I don't know what size integers they are so I'm +unsure how real of a risk that is, but it seemed worth mentioning here. + +<h2>So you've parsed the stats, now to graphs!</h2> + +My main trouble here was selecting a range that makes sense for +the data it's representing. + +Again, memory was easy. There is a +total, normally-unchanging amount of RAM, so I just use that as +the max. Perhaps there's something to be said about zooming further +in to see the megabyte-by-megabyte variance, but I am much more +interested in a "how close am I to the ceiling" kind of graph. Like, +would I hit my head if I jumped? that kind of thing. + +The CPU graph, though, that's very variable and a bit spiky. +I don't <i>really</i> care what the max value was if it's a spike, +it can go off the top for all I care, what I want to see is the +typical usage. + +If I just ranged to the max then I'd have what I call The Linode +Problem. I call it that, rather predictably, because that's what +Linode's graphs do and it makes them kind of useless? Great, I love +to see that spike up to 100%, but that's <i>all</i> that I can see now. + +So instead of max-grabbing, I sort the data and take the value that's +<i>almost</i> max. My series are 256 samples long, so what this looked +like was taking the 240th value in the array, getting the closest-highest +percent, and using that as the top of the range. + +This <i>does</i> mean if it's <i>very</i> spiky, I get The Linode Problem +again, but in that case I'm kind of okay with it. I sample every minute, +so my 256 pixel long graphs are roughly 4 hours long. If it spikes more +than 16 times in that period, perhaps that's worth looking into. + +Okay, CPU done. Network time! It's the same, pretty much. Where there was +one line, there are now two. And lots more spikes! I combine the receive +and transmit series into one <code>vec</code>, sort it, and take the 32nd +highest value. + +I draw the area under the line, too, because it was nigh impossible to see +the line when it was so.. discontinuous? We get another problem with that, +though, where the second-drawn line-and-underfill will obscure the one +drawn first. So then, to not overdraw an entire measurement, I try to draw +the average-larger one first. Which is to say, I take the average of both +series separately and draw the one with the bigger average first. That way +the smaller one will hopefully nestle under the larger, like a baby bird +hiding from the rain under their parents wing. + +<hr class="asterism-dash" /> + +That's how the range selection works, anyway. + +The graphs themselves are drawn on 256x160 gif because i like gif, 256 is +a good number, and they seem to compress better than png in this use case. + +One day I'd love to try and generate alternative text to describe +the general look of the graph. "The memory usage is steady at 300MB", +or something like "The network usage is variable, but averages 15.4kbps". + +That's it!<br /> +bye :) \ No newline at end of file |