On 02.11.2020 14:59, Jürgen Groß wrote: > On 02.11.20 14:52, Jan Beulich wrote: >> On 02.11.2020 14:41, Jürgen Groß wrote: >>> On 20.10.20 11:28, Jan Beulich wrote: >>>> On 16.10.2020 12:58, Juergen Gross wrote: >>>>> @@ -360,7 +352,7 @@ static long >>>>> evtchn_bind_interdomain(evtchn_bind_interdomain_t *bind) >>>>> if ( rc ) >>>>> goto out; >>>>> >>>>> - flags = double_evtchn_lock(lchn, rchn); >>>>> + double_evtchn_lock(lchn, rchn); >>>> >>>> This introduces an unfortunate conflict with my conversion of >>>> the per-domain event lock to an rw one: It acquires rd's lock >>>> in read mode only, while the requirements here would not allow >>>> doing so. (Same in evtchn_close() then.) >>> >>> Is it a problem to use write mode for those cases? >> >> "Problem" can have a wide range of meanings - it's not going to >> be the end of the world, but I view any use of a write lock as >> a problem when a read lock would suffice. This can still harm >> parallelism. > > Both cases are very rare ones in the life time of an event channel. I > don't think you'll ever be able to measure any performance impact from > switching these case to a write lock for any well behaved guest.
I agree as far as the lifetime of an individual port goes, but we're talking about the per-domain lock here. (Perhaps my choice of context in your patch wasn't the best one, as there it is the per-channel lock of which two instances get acquired. I'm sorry if this has lead to any confusion.) Jan
