Messages in this thread | | | Date | Thu, 25 Aug 2016 16:07:25 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v6] x86/hpet: Reduce HPET counter read contention |
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On 08/25/2016 02:50 PM, Dave Hansen wrote: > On 08/12/2016 05:59 PM, Waiman Long wrote: >> + * The lock and the hpet value are stored together and can be read in a >> + * single atomic 64-bit read. It is explicitly assumed that arch_spinlock_t >> + * is 32 bits in size. > This requirement forces us to give up all of the goodness of lockdep. > Is this strictly a performance optimization or is there some function > requirement behind it as well?
Yes, it is mostly performance optimization. Using a full spinlock will require additional synchronization code like a memory barrier to prevent race between the lock and HPET value with respect to the readers.
It is a simple lock that won't have additional locks nested inside. So I wonder if there is any value in having the lockdep functionality for this lock.
Cheers, Longman
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