Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now
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The speed at which a program runs

0
votes
Assuming perf works on your system (it just falls over on my old laptop), you can get more fine-grained CPU accounting, which shows % of the total, i.e. ignores all your idle time so you'll get nice b …
answered Jun 9 '16 by sourcejedi
3
votes
GiB) copied, 3.87044 s, 3.9 GB/s taskset: Interrupt Performance counter stats for 'taskset 0x1 sh -c dd bs=1M </dev/zero|dd bs=1M >/dev/null': 3872.597645 task-clock (msec … Performance counter stats for 'sh -c dd bs=1M </dev/zero|dd bs=1M >/dev/null': 3736.056509 task-clock (msec) # 0.873 CPUs utilized 218,047 context-switches …
answered Apr 22 '18 by sourcejedi
2
votes
1answer
) copied, 5.0566 s, 3.8 GB/s Performance counter stats for 'taskset 0x1 sh -c dd if=/dev/zero bs=1M | dd bs=1M of=/dev/null': 5059.273255 task-clock:u (msec) # 1.000 CPUs utilized … , 1.7 GB/s 6636+0 records in 6636+0 records out 6958350336 bytes (7.0 GB, 6.5 GiB) copied, 4.0492 s, 1.7 GB/s sh: Interrupt Performance counter stats for 'sh -c dd if=/dev/zero bs=1M | dd bs=1M of …
asked Apr 22 '18 by sourcejedi
2
votes
will that not be a trivial? Assume direct IO, as required for iodepth= to work. A sequential job with iodepth=2 will submit two sequential IO requests at a time. A sequential job with numjobs=2 …
answered Jul 29 '18 by sourcejedi
2
votes
-monitor might not be a good choice for this. I think it does not really show enough). Sometimes when you have a performance problem, you need to look at disk reads & writes instead. You could use sudo …
answered Jun 14 by sourcejedi
4
votes
Lookup tpacket_rcv: it's in af_packet.c. AF_PACKET means tcpdump. It looks like someone else saw a problem triggered by tcpdump, without resolution: https://groups.google.com/forum/#!msg/mechanical- …
answered Apr 16 '16 by sourcejedi
1
vote
1answer
I have a test case for journalctl where it spends several seconds reading from the disk. But if I try to benchmark multiple runs of the test case, I find that it's impossibly fast after the first run …
asked Jan 28 '18 by sourcejedi
2
votes
to improve the performance of synchronous writes, i.e. avoid writes to filesystem metadata which require a disk seek. You can illustrate this by modifying test-program.py to pre-write some data … different performance profiles. Specifically, this would not work if they are implemented using copy-on-write like btrfs. Code change: # Try to pre-allocate space if alloc: - fallocate …
answered Sep 15 '18 by sourcejedi
6
votes
automatically. Unless you're very unusual, you don't need e4defrag. The TRIM stuff is more relevant. It got turned off by default because the performance story at the time was really unclear (i.e …
answered May 27 '13 by sourcejedi
6
votes
block size, in order to get good performance. Here is an example: dd if=/dev/usbdisk1 of=/dev/usbdisk2 oflag=direct bs=32M status=progress NOTE: Sometimes you might want to pipe a disk image from … another program, such as gunzip. In this case, good performance also depends on iflag=fullblock and piping through another dd command. There is a full example in the answer here: Why does a gunzip to dd …
answered Oct 9 '18 by sourcejedi
0
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1answer
My system becomes much, much less responsive, every time I clone a VM image. I'm using virt-manager, and I can see the IO is performed by several qemu-img convert threads. I tried to gather some info …
asked Nov 5 '18 by sourcejedi
0
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vmstat is the traditional Linux command to track memory, swap and IO. E.g. vmstat 5 will print a line of statistics every 5 seconds. atop is a newer tool, which is very powerful. Running atop looks …
answered Nov 5 '18 by sourcejedi
1
vote
Many of the commands you want "do one thing, and do it well". On the one hand, this means they all look a bit different. On the bright side, this can make it more manageable - to learn one thing at …
answered Jul 1 by sourcejedi
4
votes
Note that Linux gained a zRAM feature sometime in the past few years. It's a compressed ramdisk that can be used for swap space, i.e. to compress inactive memory content. The Gentoo Wiki entry on it …
answered Aug 1 '15 by sourcejedi
17
votes
The usual reason for hitting this issue, is that the process is blocking in page faults. These are reads or possibly writes to files performed through a memory mapping aka mmap(). You may have notic …
answered Jan 28 '18 by sourcejedi

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