Re: ext3 IO latency measurements (was: Linux 2.6.29)

Ingo Molnar
2009-03-26T12:46:44Z

[-- Attachment #1: Type: text/plain, Size: 2139 bytes --]

* Theodore Tso <tytso@mit.edu> wrote:

> > while :; do
> > date
> > make mrproper 2>/dev/null >/dev/null
> > make defconfig 2>/dev/null >/dev/null
> > make -j32 bzImage 2>/dev/null >/dev/null
> > done &
> ^^
>
> So there would have been nothing to ^C; I assume you were running
> this with a variant that didn't have the ampersand, which would
> have run the whole shell pipeline in a detached background
> process?

That was just the example - the real script did not go into the
background so it was Ctrl-C-able. I've attached it.

> In any case, the workaround for this is to ^Z the script, and then
> "kill %" it.
>
> I'm pretty sure this is actually a bash problem. When you send a
> Ctrl-C, it sends a SIGINT to all of the members of the tty's
> foreground process group. Under some circumstances, bash sets the
> signal handler for SIGINT to be SIGIGN. I haven't looked at this
> super closely (it would require diving into the bash sources), but
> you can see it if you attach an strace to the bash shell driving a
> script such as
>
> #!/bin/bash
>
> while /bin/true; do
> date
> sleep 60
> done &
>
> If you do a "ps axo pid,ppid,pgrp,args", you'll see that the bash
> and the sleep 60 have the same process group. If you emulate
> hitting ^C by sending a SIGINT to pid of the shell, you'll see
> that it ignores it. Sleep also seems to be ignoring the SIGINT
> when run in the background; but it does honor SIGINT in the
> foreground --- I didn't have time to dig into that.
>
> In any case, bash appears to SIGIGN the INT signal if there is a
> child process running, and only takes the ^C if bash itself is
> actually "running" the shell script. For example, if you run the
> command "date;sleep 10;date;sleep 10;date", the ^C only interrupts
> the sleep command. It doesn't stop the series of commands which
> bash is running.

It happens all the time - and it does look like a Bash bug. I
reported it to the Bash maintainer one or two years ago. He said
he does not see it as he's using MacOS X. Can dig into archives if
needed.

Ingo

[-- Attachment #2: compile-test --]
[-- Type: text/plain, Size: 321 bytes --]

#
# Cool down caches as much as possible:
#
sync
echo 3 > /proc/sys/vm/drop_caches

#
# Kernel developer builds his kernel workload:
#
while :; do
date
make mrproper 2>/dev/null >/dev/null
make defconfig 2>/dev/null >/dev/null
make -j32 bzImage 2>/dev/null >/dev/null
done