Re: Good news for threading!

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

Kay Sievers wrote:
> On Mon, May 25, 2009 at 15:46, Alan Jenkins <alan-jenkins@tuffmail.co.uk> wrote:
>   
>> I solved one of the reservations that held me back on threaded udevd.  I
>> still have some other concerns to work on, but I'm feeling much more
>> optimistic now.
>>
>> Replacing processes with threads reduced page faults (copy-on-write) by
>> 60-80%, but that _still_ left over 10% of udevd time in page fault overhead.
>>
>> I've discovered I can reduce this overhead much further by marking thread
>> stacks with MADV_DONTFORK.  When a thread needs to fork an external program,
>> it can temporarily unmark its own thread stack.
>>
>> Disclaimer: I have no idea why this should reduce the number of page faults.
>>  I could be getting something horribly wrong.  But even if it's wrong, at
>> least it gives me a new angle on this problem.
>>     
>
> Do you have numbers for the difference of threaded vs. non-threaded, for:
>   time (udevadm trigger; udevadm settle)
> when no rules are active?
>
> On my box it's ~0.6 seconds for the non-threaded udevd and ~460
> devices, when I move all rules out of the way.
>
> Thanks,
> Kay
>   

Interesting question.  I stop HAL first, it tends to slow my tests down 
and doesn't represent normal bootup.

Test machine is eeepc 701; trigger -n shows 382 devices.

no threading:    ~0.5s
threading:   ~0.25s

This is based on an a slightly out of date tree.  Your latest HEAD is 
still ~0.5s, but perhaps slightly lower, 0.46-0.48 as opposed to 0.48-0.5.

Alan