Messages in this thread | | | Subject | Re: 2.5isms | From | Andi Kleen <> | Date | Sat, 01 Jan 2005 10:13:41 +0100 |
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Nick Piggin <nickpiggin@yahoo.com.au> 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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