Re: 2.5isms

[Andi Kleen <ak@xxxxxx>]

Nick Piggin <nickpiggin@xxxxxxxxxxxx> writes:

> Justin Pryzby wrote:
>> Hi all, I have more 2.5isms for the list.  ./fs/binfmt_elf.c:
>>   #ifdef CONFIG_X86_HT
>>                   /*
>>                    * In some cases (e.g. Hyper-Threading), we want to avoid L1
>>                    * evictions by the processes running on the same package. One
>>                    * thing we can do is to shuffle the initial stack for them.
>>                    *
>>                    * The conditionals here are unneeded, but kept in to make the
>>                    * code behaviour the same as pre change unless we have
>>                    * hyperthreaded processors. This should be cleaned up
>>                    * before 2.6
>>                    */
>>                   if (smp_num_siblings > 1)
>>                           STACK_ALLOC(p, ((current->pid % 64) << 7));
>>   #endif
>>
>
> Can we just kill it? Or do it unconditionally? Or maybe better yet, wrap
> it properly in arch code?

You can't kill it without ruining performance on older HT CPUs.
I would just keep it, it fixes the problem perhaps with a small amount of 
code. A more generalized #ifdef may be a good idea (NEED_STACK_RANDOM)
may be a good idea, but it is not really a pressing need. Enabling 
it unconditionally may be an option, although it will make it harder
to repeat test runs on non hyperthreaded CPUs.

-Andi

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