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Message-ID: <Yy/usWIjvzHGNq0b@unreal> Date: Sun, 25 Sep 2022 09:01:21 +0300 From: Leon Romanovsky <leon@...nel.org> To: Saeed Mahameed <saeedm@...dia.com> Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org, Paolo Abeni <pabeni@...hat.com> Subject: Re: [PATCH net-next] net/mlx5: Make ASO poll CQ usable in atomic context On Sat, Sep 24, 2022 at 01:11:31PM -0700, Saeed Mahameed wrote: > On 24 Sep 21:51, Leon Romanovsky wrote: > > On Sat, Sep 24, 2022 at 10:24:25AM -0700, Saeed Mahameed wrote: > > > On 24 Sep 14:17, Leon Romanovsky wrote: > > > > From: Leon Romanovsky <leonro@...dia.com> > > > > > > > > Poll CQ functions shouldn't sleep as they are called in atomic context. > > > > The following splat appears once the mlx5_aso_poll_cq() is used in such > > > > flow. > > > > > > > > BUG: scheduling while atomic: swapper/17/0/0x00000100 > > > > > > ... > > > > > > > /* With newer FW, the wait for the first ASO WQE is more than 2us, put the wait 10ms. */ > > > > - err = mlx5_aso_poll_cq(aso, true, 10); > > > > + expires = jiffies + msecs_to_jiffies(10); > > > > + do { > > > > + err = mlx5_aso_poll_cq(aso, true); > > > > + } while (err && time_is_after_jiffies(expires)); > > > > mutex_unlock(&flow_meters->aso_lock); > > > ^^^^ > > > busy poll won't work, this mutex is held and can sleep anyway. > > > Let's discuss internally and solve this by design. > > > > This is TC code, it doesn't need atomic context and had mutex + sleep > > from the beginning. > > > > then let's bring back the sleep for TC use-case, we don't need to burn the > CPU! Again, this is exactly how TC was implemented. The difference is that before it burnt cycles in poll_cq and now it does it inside TC code. > But still the change has bigger effect on other aso use cases, see below. I have serious doubts about it. > > > My change cleans mlx5_aso_poll_cq() from busy loop for the IPsec path, > > so why do you plan to change in the design? > > > > a typical use case for aso is > > post_aso_wqe(); > poll_aso_cqe(); > > The HW needs time to consume and excute the wqe then generate the CQE. > This is why the driver needs to wait a bit when polling for the cqe, > your change will break others. Let's discuss internally. IPsec was always implemented without any time delays, and I'm sure that MACsec doesn't need too, it is probably copy/paste. More generally, post_wqe->poll_cq is very basic paradigm in RDMA and delays were never needed. But if you insist, let's discuss internally. Thanks > > > Thanks
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