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Date: Mon, 10 Sep 2018 10:15:50 -0700 From: Davidlohr Bueso <dave@...olabs.net> To: Waiman Long <longman@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] locking/rwsem: Make owner store task pointer of last owning reader On Mon, 10 Sep 2018, Waiman Long wrote: >One major issue with a combined count/owner is that we may have to use >cmpxchg for reader lock which will certainly impact reader-heavy >workloads. I have also thought about ways to compress the task pointer >address so that it can use fewer bits and leave the rests for reader >count. It is probably doable on 64-bit systems, but likely not on 32-bit >system given that there are less bits to play around. Yeah we've discussed this before. As a cleanup it would obviously be good, but I fear about raw performance loss when using cmpxchg instead of xadd. Thanks, Davidlohr
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