Messages in this thread | | | Subject | Re: [PATCH 7/8] x86/apic: Make cpu_mask_to_apicid() operations return error code | From | Suresh Siddha <> | Date | Thu, 07 Jun 2012 15:24:05 -0700 |
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On Thu, 2012-06-07 at 15:15 +0200, Alexander Gordeev wrote: > Current cpu_mask_to_apicid() and cpu_mask_to_apicid_and() > implementations have few shortcomings: > > 1. A value returned by cpu_mask_to_apicid() is written to hardware > registers unconditionally. Should BAD_APICID get ever returned it will > be written to a hardware too. But the value of BAD_APICID is not > universal across all hardware in all modes and might cause unexpected > results, i.e. interrupts might get routed to CPUs that are not > configured to receive it. > > 2. Because the value of BAD_APICID is not universal it is counter- > intuitive to return it for a hardware where it does not make sense > (i.e. x2apic). > > 3. cpu_mask_to_apicid_and() operation is thought as an complement to > cpu_mask_to_apicid() that only applies a AND mask on top of a cpumask > being passed. Yet, as consequence of 18374d8 commit the two operations > are inconsistent in that of: > cpu_mask_to_apicid() should not get a offline CPU with the cpumask > cpu_mask_to_apicid_and() should not fail and return BAD_APICID > These limitations are impossible to realize just from looking at the > operations prototypes. > > Most of these shortcomings are resolved by returning a error code > instead of BAD_APICID. As the result, faults are reported back early > rather than possibilities to cause a unexpected behaviour exist (in case > of [1]). > > The only exception is setup_timer_IRQ0_pin() routine. Although obviously > controversial to this fix, its existing behaviour is preserved to not > break the fragile check_timer() and would better addressed in a separate > fix. >
I am ok with these changes. But even better would be to remove the cpu_mask_to_apicid() and just use cpu_mask_to_apicid_and() instead.
Looks like there are only two places cpu_mask_to_apicid() being used anyways. So instead of patches 7 and 8, can you remove cpu_mask_to_apicid() in patch-7 and fixup the return value of cpu_mask_to_apicid_and() in patch-8
thanks, suresh
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