On 03/14/17 12:01, H. Peter Anvin wrote:
> On 11/08/16 10:39, Kyle Huey wrote:
>> }
>>
>> + if (test_tsk_thread_flag(prev_p, TIF_NOCPUID) ^
>> + test_tsk_thread_flag(next_p, TIF_NOCPUID)) {
>> + set_cpuid_faulting(test_tsk_thread_flag(next_p, TIF_NOCPUID));
>> + }
>> +
>> if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
>> test_tsk_thread_flag(next_p, TIF_NOTSC)) {
>> /* prev and next are different */
>> if (test_tsk_thread_flag(next_p, TIF_NOTSC))
>> hard_disable_TSC();
>> else
>> hard_enable_TSC();
>> }
>
> I'm unhappy about this part: we already do two XORs on these after bit
> extraction, which is quite inefficient; and at least theoretically we
> could be indirecting though the ->stack pointer for every one if gcc
> can't tell it won't have changed (we really need to get thread_info
> moved into the task_struct allocation and away from the kernel stack,
> especially since on x86 the pointer is the same size as the vestigial
> structure it points to.)
>
Nevermind, I was accidentally looking at v10 not v15 of this patchset.
My bad.
-hpa
