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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Jiri Pirko , Sebastian Andrzej Siewior , Lorenzo Bianconi , Daniel Borkmann , open list Subject: Re: [RFC net-next 1/6] netdevice: Add napi_affinity_no_change Message-ID: References: <20240812145633.52911-1-jdamato@fastly.com> <20240812145633.52911-2-jdamato@fastly.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On 08/12, Joe Damato wrote: > On Mon, Aug 12, 2024 at 01:23:27PM -0700, Stanislav Fomichev wrote: > > On 08/12, Joe Damato wrote: > > > Several drivers have their own, very similar, implementations of > > > determining if IRQ affinity has changed. Create napi_affinity_no_change > > > to centralize this logic in the core. > > > > > > This will be used in following commits for various drivers to eliminate > > > duplicated code. > > > > > > Signed-off-by: Joe Damato > > > --- > > > include/linux/netdevice.h | 8 ++++++++ > > > net/core/dev.c | 14 ++++++++++++++ > > > 2 files changed, 22 insertions(+) > > > > > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h > > > index 0ef3eaa23f4b..dc714a04b90a 100644 > > > --- a/include/linux/netdevice.h > > > +++ b/include/linux/netdevice.h > > > @@ -464,6 +464,14 @@ enum rx_handler_result { > > > typedef enum rx_handler_result rx_handler_result_t; > > > typedef rx_handler_result_t rx_handler_func_t(struct sk_buff **pskb); > > > > > > +/** > > > + * napi_affinity_no_change - determine if CPU affinity changed > > > + * @irq: the IRQ whose affinity may have changed > > > + * > > > + * Return true if the CPU affinity has NOT changed, false otherwise. > > > + */ > > > +bool napi_affinity_no_change(unsigned int irq); > > > + > > > void __napi_schedule(struct napi_struct *n); > > > void __napi_schedule_irqoff(struct napi_struct *n); > > > > > > diff --git a/net/core/dev.c b/net/core/dev.c > > > index 751d9b70e6ad..9c56ad49490c 100644 > > > --- a/net/core/dev.c > > > +++ b/net/core/dev.c > > > @@ -89,6 +89,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > #include > > > #include > > > #include > > > @@ -6210,6 +6211,19 @@ void __napi_schedule_irqoff(struct napi_struct *n) > > > } > > > EXPORT_SYMBOL(__napi_schedule_irqoff); > > > > > > +bool napi_affinity_no_change(unsigned int irq) > > > +{ > > > + int cpu_curr = smp_processor_id(); > > > + const struct cpumask *aff_mask; > > > + > > > > [..] > > > > > + aff_mask = irq_get_effective_affinity_mask(irq); > > > > Most drivers don't seem to call this on every napi_poll (and > > cache the aff_mask somewhere instead). Should we try to keep this > > out of the past path as well? > > Hm, I see what you mean. It looks like only gve calls it on every > poll, while the others use a cached value. > > Maybe a better solution is to: > 1. Have the helper take the cached affinity mask from the driver > and return true/false. > 2. Update gve to cache the mask (like the other 4 are doing). SG! GVE is definitely the outlier here. > FWIW, it seems i40e added this code to solve a specific bug [1] and > I would assume other drivers either hit the same issue (or were > inspired by i40e). > > In general: I think the logic is here to stay and other drivers may > do something similar in the future. +1 on pushing this logic to the core if possible. > It'd be nice to have one helper instead of several different > copies/implementations. > > [1]: https://patchwork.ozlabs.org/project/intel-wired-lan/patch/1473895479-23035-9-git-send-email-bimmy.pujari@intel.com/