On 11/21/2011 10:17 PM, Tejun Heo wrote:
> Hello, Rafael.
>
> On Sat, Nov 19, 2011 at 10:57:19PM +0100, Rafael J. Wysocki wrote:
>>> + while (!mutex_trylock(&pm_mutex)) {
>>> + try_to_freeze();
>>> + msleep(10);
>>
>> The number here seems to be somewhat arbitrary. Is there any reason not to
>> use 100 or any other number?
>
> This is a bit moot at this point but, at least for me, yeah, it's a
> number I pulled out of my ass. That said, I think it's a good number
> to pull out of ass for userland visible retry delays for the following
> reasons.
>
> * It's a good number - 10! which happens to match the number of
> fingers I have! Isn't that just weird? @.@
>
> * For modern hardware of most classes, repeating not-so-complex stuff
> every 10ms for a while isn't taxing (or even noticeable) at all.
>
> * Sub 10ms delays usually aren't noticeable to human beings even when
> several of them are staggered. This is very different when you get
> to 100ms range.
>
> ie. going from 1ms to 10ms doesn't cost you too much in terms of human
> noticeable latency (for this type of situations anyway) but going from
> 10ms to 100ms does. In terms of computational cost, the reverse is
> somewhat true too. So, yeah, I think 10ms is a good out-of-ass number
> for this type of delays.
>
My God! I had absolutely no idea you had cooked up that number just like
that ;-) Look at how creative I was when defending that number :P
Your justification is not bad either ;-)
[ Well, seriously, I had given a fair amount of thought before incorporating
that number in my patch, by looking at the freezer re-try latency and so on,
which I explained in my reply earlier.]
Anyways, nice one :-)
Thanks,
Srivatsa S. Bhat
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