On Tue, 2024-02-06 at 20:22 -0800, Sean Christopherson wrote: > On Mon, Jan 15, 2024, Paul Durrant wrote: > > From: Paul Durrant <pdurrant@xxxxxxxxxx> > > > > Taking a write lock on a pfncache will be disruptive if the cache is > > *Unnecessarily* taking a write lock. No. Taking a write lock will be disrupting. Unnecessarily taking a write lock will be unnecessarily disrupting. Taking a write lock on a Thursday will be disrupting on a Thursday. But the key is that if the cache is heavily used, the user gets disrupted. > Please save readers a bit of brain power > and explain that this is beneificial when there are _unrelated_ invalidation. I don't understand what you're saying there. Paul's sentence did have an implicit "...so do that less then", but that didn't take much brain power to infer. > > heavily used (which only requires a read lock). Hence, in the MMU notifier > > callback, take read locks on caches to check for a match; only taking a > > write lock to actually perform an invalidation (after a another check). > > This doesn't have any dependency on this series, does it? I.e. this should be > posted separately, and preferably with some performance data. Not having data > isn't a sticking point, but it would be nice to verify that this isn't a > pointless optimization. No fundamental dependency, no. But it was triggered by the previous patch, which makes kvm_xen_set_evtchn_fast() use read_trylock() and makes it take the slow path when there's contention. It lives here just fine as part of the series.
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