On Fri, Mar 20, 2009 at 4:44 PM, Bruce Dubbs <[email protected]> wrote:
> Dan Nicholson wrote:
>> On Fri, Mar 20, 2009 at 11:15 AM, Bruce Dubbs <[email protected]> wrote:
>>> Dan Nicholson wrote:
>>>
>>>> A while back I sanitized the bootscripts for POSIX sh compatibility, and
>>>> I think DJ has been maintaining that goal. I think it's a nice (and
>>>> obtainable) goal to target since having sh != bash can save on bloat.
>>> Save on bloat? For what? My copy of bash is 500K. dash is about 80K.
>>
>> Right, bash is 4 times the size of dash. That adds up when you're forking the
>> shell a hundred times or whatever during boot.
>
> Come on Dan. You know better than that. When you fork a program, the code
> segment is not duplicated, but only any necessary data. For that, there would
> be no significant difference between bash and dash.
I don't honestly know how much memory is duplicated or not. Here's a
loop of shells that simply fork, do nothing and exit.
$ time { for n in {0..100}; do /bin/bash -c :; done; }
real 0m0.431s
user 0m0.227s
sys 0m0.191s
$ time { for n in {0..100}; do /bin/dash -c :; done; }
real 0m0.159s
user 0m0.048s
sys 0m0.120s
Clearly, it is taking more time for the bash shell. I know you are
going to say we're only talking about hundredths of seconds for each
run, so why should we care. But it's more than double relatively.
If you were looking at a system (not just a computer system) and you
found that one part took twice the resources and twice as long to
start up as another part offering similar functionality, why would you
dismiss it? Maybe the original part offers better features than the
replacement, but that doesn't mean the other facts can be ignored.
>> The last time I tested, it shaved like 4 seconds off boot using dash instead
>> of bash.
>>
>> http://linuxfromscratch.org/pipermail/lfs-support/2008-February/034192.html
>
>> I use bash all the time and I wouldn't consider using a minimal posix shell
>> for my login shell. For any non-trivial script, I use bash. However, for a
>> generic shell script, I don't know why you couldn't make it posix compliant.
>> That allows people to have flexibility without much loss. The bootscripts are
>> pretty simple.
>
> As you mention, bootscripts are pretty simple and in no way are a stress test.
> Four seconds doesn't seem very significant to me. It's not enough to notice
> unless you are doing a timing test.
4 seconds out of 18 total is something I consider very significant.
For you, maybe it's not, but you are free to keep /bin/bash as
/bin/sh. However, you agree that the bootscripts are simple, so why do
you need to use bash again?
Let's just forget about it. I think this is the second or third time
we've had this conversation and I think we just say the same things
back and forth.
--
Dan
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