Re: [PATCH] libudev: Allocate udev_device->envp lazily

[Alan Jenkins <alan-jenkins@tuffmail.co.uk>]

Kay Sievers wrote:
> On Tue, Oct 21, 2008 at 12:11, Alan Jenkins <alan-jenkins@tuffmail.co.uk> wrote:
>   
>> Allocate udev_device->envp lazily
>>
>> It's a pity to allocate 128 words when we don't need them.
>> Measured 2% _user_ cpu time reduction on EeePC coldplug.
>>     
>
> Any idea what might take 2% here? We don't do anything if the envp
> isn't used. We do almost the same thing with or without the patch
> besides that "struct udev_device" is 1016 bytes smaller now, and we
> malloc() it.
>
> Kay
>   

oprofile said malloc() went down by about that much.  I measured on top
of threaded udevd, so I might be unlucky and chasing overheads you don't
see in the single-threaded implementation :).

By rights it should reduce memset() (or calloc now).  And it might help
with caching, because the array effectively splits udev_device in two.

Using memory more compactly can reduce page faults, but I don't think
that was significant.

Alan