Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

[Linus Torvalds]

On Thu, Nov 11, 2010 at 11:08 AM, Mike Galbraith <efault@xxxxxx> wrote:
>
>>  - the reason I suggested the signal struct was really that I thought
>> it would avoid extra (unnecessary) cost in thread creation/teardown.
>>
>>    Maybe I should have made that clear, but this seems to
>> unnecessarily do the whole atomic_inc/dec for each thread. That seems
>> a bit sad.
>>
>>    That said, if not having to dereference ->signal simplifies the
>> scheduler interaction, I guess the extra atomic ref at thread
>> creation/deletion is fine. So I don't think this is wrong, it's just
>> something I wanted to bring up.
>
> Ah, ok.  Anything that cuts overhead is worth doing.

Well, it cuts both ways. Maybe your approach is simpler and avoids
overhead at scheduling time. And "tsk->signal" may not be reliable due
to races with exit etc, so it may well be that going through the
signal struct could end up being a source of nasty races. I didn't
look whether the scheduler already derefenced ->signal for some other
reason, for example.

So your patch may well have done the exact right thing.

                              Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/