Comments on: strace: The Friend You Never Knew You Had

By: Salman

Salman — Fri, 10 Feb 2012 10:47:01 +0000

I let ppeloe tell me what to write about sometimes. You don’t have to write about everything, just find your own thing to be comfortable with and the blog will nearly write itself.

By: gserban

gserban — Wed, 30 Nov -0001 00:00:00 +0000

Cool. I actually had no idea this command existed.

By: parmando

parmando — Wed, 30 Nov -0001 00:00:00 +0000

Muy bueno, me di cuenta de varias cosas que pasaba por alto al ver la salida de strace!!

By: porridge

porridge — Wed, 30 Nov -0001 00:00:00 +0000

There is ‘ltrace’ as well. More useful sometimes.

By: ohmay

ohmay — Wed, 30 Nov -0001 00:00:00 +0000

And for such "small" writes, how interacts the buffer-cache? In the article it is said that the difference between write rates are because the latency of the drive, the speed of the drive and this kind of things.

Buf for small writes the data writed shouldn't be writed on buffer-cache?, and because of that at memory speed? Perhaps I'm wrong, but I think that the difference between write rates might be related to the initialization of I/O functions.

In any case, great article.

By: tombauer

tombauer — Wed, 30 Nov -0001 00:00:00 +0000

I think an interesting question would be why does the compiler create code that does the write with two write system calls. Why not one? And what is special about 388K? Hmmm.

By: tothzp

tothzp — Wed, 30 Nov -0001 00:00:00 +0000

1. A pretty big amount of data can be written to the buffer cache first. So when write() returns you don't know if the data has been physically written to the disk or not. (Except if you flush your file to disk, e.g. with the fsync() or fdatasync() function.)

2. strace can be also used to collect statistics about the time spent in different system calls. Use the -c option for that:

# strace -p 16640 -c Process 16640 attached - interrupt to quit Process 16640 detached % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 36.72 0.649557 36 17944 epoll_wait 33.40 0.590959 7 85036 gettimeofday 21.75 0.384777 16 23568 writev 6.65 0.117595 6 19767 recv 1.48 0.026198 8 3354 time ------ ----------- ----------- --------- --------- ---------------- 100.00 1.769086 149669 total