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Groups > linux.kernel > #1461473
| From | Dave Hansen <dave.hansen@intel.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v5] x86/hpet: Reduce HPET counter read contention |
| Date | 2016-08-12 23:50 +0200 |
| Message-ID | <s5suZ-7jU-3@gated-at.bofh.it> (permalink) |
| References | <s5sbD-7aC-11@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 08/12/2016 02:25 PM, Waiman Long wrote:
> + do {
> + cpu_relax();
> + new.lockval = READ_ONCE(hpet.lockval);
> + } while ((new.value == old.value) && raw_spin_is_locked(&new.lock));
While it gets more far-fetched, this isn't guaranteed to make progress
until the saved HPET value actually changes. You could have a constant
stream of other CPUs going and doing hpet_readl() (and getting the same
value back from a sloooow HPET). So each time through this loop, this
processor sees (new.value == old.value), and sees the lock held.
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[PATCH v5] x86/hpet: Reduce HPET counter read contention Waiman Long <Waiman.Long@hpe.com> - 2016-08-12 23:30 +0200 Re: [PATCH v5] x86/hpet: Reduce HPET counter read contention Dave Hansen <dave.hansen@intel.com> - 2016-08-12 23:40 +0200 Re: [PATCH v5] x86/hpet: Reduce HPET counter read contention Dave Hansen <dave.hansen@intel.com> - 2016-08-12 23:50 +0200
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