kern.timecounter.smp_tsc_adjust

[Alexander Motin]

On 04.06.2014 20:50, Jung-uk Kim wrote:
> On 2014-06-04 13:32:13 -0400, Chris Torek wrote:
>>> In any case, at least one, and maybe two, routines need their
>>> types changed (and maybe the TSC_READ macro as well).  Is it OK
>>> to just assume the upper 32 bits are in sync?
>>
>> For whatever it may be worth, the following patch (to change
>> everything to 64 bits) is boot-tested and no longer crashes the
>> system that did crash with the unpatched version.  It also
>> successfully synchronized TSCs at least once (Intel based board
>> with the "invariant TSC" bit set, 40 CPUs).
>>
>> Chris
>>
>> x86/tsc: fix SMP TSC adjustment code
>>
>> On SMP systems, if kern.timecounter.smp_tsc is set, the kernel
>> attempts to determine whether the TSCs on the processors are
>> sufficiently in-sync to be used for time counting.  If not, and
>> kern.timecounter.smp_tsc_adjust is set, we then attempt to adjust
>> all the TSCs.
>>
>> The adjustment code assumed we kept a full 64-bit value for each
>> TSC, but the data-gathering and comparison code used 32-bit values.
>> As a result, if the timecounters were out of sync, the adjustment
>> code could crash (depending on the number of CPUs).
>>
>> This converts everything to full 64-bit values.
> ...
>
> It was done on head almost two years ago:
>
> http://svnweb.freebsd.org/changeset/base/239133
>
> I guess mav forgot to MFC r239133 before r250772 (CC'ed):
>
> http://svnweb.freebsd.org/changeset/base/250772

Merged to stable/9. Thanks for the reminder.

-- 
Alexander Motin