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Date: Wed, 6 Feb 2019 14:51:47 -0800 From: Cong Wang <xiyou.wangcong@...il.com> To: Saeed Mahameed <saeedm@...lanox.com> Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Tariq Toukan <tariqt@...lanox.com> Subject: Re: [Patch net-next] mlx5: use RCU lock in mlx5_eq_cq_get() On Wed, Feb 6, 2019 at 9:40 AM Saeed Mahameed <saeedm@...lanox.com> wrote: > > On Wed, 2019-02-06 at 09:35 -0800, Saeed Mahameed wrote: > > On Tue, 2019-02-05 at 16:35 -0800, Cong Wang wrote: > > > mlx5_eq_cq_get() is called in IRQ handler, the spinlock inside > > > gets a lot of contentions when we test some heavy workload > > > with 60 RX queues and 80 CPU's, and it is clearly shown in the > > > flame graph. > > > > > > In fact, radix_tree_lookup() is perfectly fine with RCU read lock, > > > we don't have to take a spinlock on this hot path. It is pretty > > > much > > > similar to commit 291c566a2891 > > > ("net/mlx4_core: Fix racy CQ (Completion Queue) free"). Slow paths > > > are still serialized with the spinlock, and with synchronize_irq() > > > it should be safe to just move the fast path to RCU read lock. > > > > > > This patch itself reduces the latency by about 50% with our > > > workload. > > > > > > Cc: Saeed Mahameed <saeedm@...lanox.com> > > > Cc: Tariq Toukan <tariqt@...lanox.com> > > > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com> > > > > Acked-by: Saeed Mahameed <saeedm@...lanox.com> > > > > Actually, the commit message needs some rework, since there is no > contention upstream, Cong can you take care of this and post a V2 ? I can't verify if upstream has contention or not, but yeah, I can at least mention the commit 02d92f7903647119e125b24f547 in changelog. Thanks.
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