Re: `make check' overworks one core on my Core2 quad

[David Kastrup]

Han-Wen Nienhuys <address@hidden> writes:

> On Sun, Dec 13, 2009 at 12:13 PM, Graham Percival
> <address@hidden> wrote:
>> On Sun, Dec 13, 2009 at 2:00 PM, Neil Puttock <address@hidden> wrote:
>>> 2009/12/13 Mark Polesky <address@hidden>:
>>>
>>>> Is there a way to improve this?  I don't want to put too
>>>> much extra stress on CPU1 if I run `make check' alot.  Or am
>>>> I being paranoid?
>>>
>>> make -j5 CPU_COUNT=5 check
>>
>> Be warned that sometimes lilypond-book has hash collisions in the
>> filename, which can lead to weird compile errors when one process
>> finished dealing with aa/lily-aaaa.ps (and thus deletes it), while
>> another process has finished generating aa/lily-aaaa.ps but hasn't
>> started running ps2pdf yet, and thus doesn't find the file that it
>> just wrote.
>
> Do you have real evidence for that?  We use 10 hex digits, yielding
> 2^40 combinations, so a 2^20 (one in a million) chance of collisions.

If we are talking about 2 particular files colliding.  If we are talking
about a collision in n files, there are n(n+1)/2 combinations all of
which have a 2^20 chance of collision (of course, those are not
independent collisions, but the approximation is pretty good).  A 1%
chance of collision is (first order approximation) achieved when
n(n+1)/2=10000, meaning n is something like 140.

Close enough to make 40 bits feel uncomfortable.

-- 
David Kastrup