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Date: Wed, 29 Mar 2017 20:50:14 +0300 From: Sagi Grimberg <sagi@...mberg.me> To: Keith Busch <keith.busch@...el.com> Cc: linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org, Thomas Gleixner <tglx@...utronix.de>, Christoph Hellwig <hch@....de> Subject: Re: [PATCH] irq/affinity: Assign all CPUs a vector > Sure, I have a 2-socket server with 16 threads each. I take one CPU > offline in socket 2, so I've 16 threads on socket 1, 15 in socket 2. In > total, 31 threads so requesting 31 vectors. > > Currently, vecs_per_node is calculated in the first iteration as 31 / 2, so 15. > > ncpus of socket 1 is 16. cpus_per_vec = 16 / 15, so 1 CPU per vector > with one extra. > > When iterating the second socket, though, vecs_per_node is incremented > from 15 to 16 (to account for the "extra" from before). However, the > ncpus is only 15, so that iteration calculates: > > cpus_per_vec = 15 / 16 > > And since that's zero, the remaining 16 vectors are not assigned to any > CPU, and the second socket has no vectors assigned to their CPUs. Thanks for the clarification, makes sense... Reviewed-by: Sagi Grimberg <sagi@...mberg.me>
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