[OE-core] Default value for FULL_OPTIMIZATION

[Mike Looijmans]

On 03-02-16 21:59, Khem Raj wrote:
> On Wed, Feb 3, 2016 at 12:57 PM, Phil Blundell <pb at pbcl.net> wrote:
>> On Wed, 2016-02-03 at 12:51 -0800, Khem Raj wrote:
>>> On Wed, Feb 3, 2016 at 12:48 PM, Phil Blundell <pb at pbcl.net> wrote:
>>>> On Tue, 2016-02-02 at 22:17 -0800, Khem Raj wrote:
>>>>> -pipe does speed up build time so its an optimization.
>>>>
>>>> How much does it really speed it up by?  I seem to recall the effect was
>>>> fairly negligible, but maybe I am remembering that wrong.
>>>
>>> it does not create files for intermediate objects so if you have slow
>>> media it can be significant
>>> but if you have SSDs then it might be diminished.
>>
>> The files go in /tmp though, right?  Even if that isn't a tmpfs, which I
>> think it is on almost all systems nowadays, they will almost certainly
>> just sit in the buffer cache and never actually get written to the
>> disk.
>
> in systems of  this age it should be yet.

In the lab, yes.

In the real world, the system may be under load. On desktop computers, /tmp/ 
is usually NOT on tmpfs.

At some point, in order to "write" to your filesystem, it will need to read it 
first (e.g. to get a free allocation spot). In that cause, the read request 
will have to get in line behind the other IO requests in the queue, and it 
suddenly might take seconds to perform that simple request. Even on SSD, this 
will happen and give a noticable drop in performance.

You might want to run that test while reading your disk (dd if=/dev/sda 
of=/dev/null) and see what happens.


Kind regards,

Mike Looijmans
System Expert

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