Re: [PATCH net-next] sfc: reduce the number of requested xdp ev queues

From: Jesper Dangaard Brouer <jbrouer@redhat.com>
To: Ivan Babrou <ivan@cloudflare.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	bpf@vger.kernel.org, kernel-team@cloudflare.com,
	Edward Cree <ecree.xilinx@gmail.com>,
	Martin Habets <habetsm.xilinx@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>
Subject: Re: [PATCH net-next] sfc: reduce the number of requested xdp ev queues
Date: Thu, 21 Jan 2021 18:11:30 +0100	[thread overview]
Message-ID: <20210121181130.77c06723@carbon> (raw)
In-Reply-To: <20210120212759.81548-1-ivan@cloudflare.com>

On Wed, 20 Jan 2021 13:27:59 -0800
Ivan Babrou <ivan@cloudflare.com> wrote:

> Without this change the driver tries to allocate too many queues,
> breaching the number of available msi-x interrupts on machines
> with many logical cpus and default adapter settings:
> 
> Insufficient resources for 12 XDP event queues (24 other channels, max 32)
> 
> Which in turn triggers EINVAL on XDP processing:
> 
> sfc 0000:86:00.0 ext0: XDP TX failed (-22)
> 
> Signed-off-by: Ivan Babrou <ivan@cloudflare.com>
> ---

I guess the patch is good in itself due to available msi-x interrupts.

Per earlier discussion: What will happen if a CPU with an ID higher
than available XDP TX-queues redirect a packet out this driver?

>  drivers/net/ethernet/sfc/efx_channels.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sfc/efx_channels.c b/drivers/net/ethernet/sfc/efx_channels.c
> index a4a626e9cd9a..1bfeee283ea9 100644
> --- a/drivers/net/ethernet/sfc/efx_channels.c
> +++ b/drivers/net/ethernet/sfc/efx_channels.c
> @@ -17,6 +17,7 @@
>  #include "rx_common.h"
>  #include "nic.h"
>  #include "sriov.h"
> +#include "workarounds.h"
>  
>  /* This is the first interrupt mode to try out of:
>   * 0 => MSI-X
> @@ -137,6 +138,7 @@ static int efx_allocate_msix_channels(struct efx_nic *efx,
>  {
>  	unsigned int n_channels = parallelism;
>  	int vec_count;
> +	int tx_per_ev;
>  	int n_xdp_tx;
>  	int n_xdp_ev;
>  
> @@ -149,9 +151,9 @@ static int efx_allocate_msix_channels(struct efx_nic *efx,
>  	 * multiple tx queues, assuming tx and ev queues are both
>  	 * maximum size.
>  	 */
> -
> +	tx_per_ev = EFX_MAX_EVQ_SIZE / EFX_TXQ_MAX_ENT(efx);
>  	n_xdp_tx = num_possible_cpus();
> -	n_xdp_ev = DIV_ROUND_UP(n_xdp_tx, EFX_MAX_TXQ_PER_CHANNEL);
> +	n_xdp_ev = DIV_ROUND_UP(n_xdp_tx, tx_per_ev);
>  
>  	vec_count = pci_msix_vec_count(efx->pci_dev);
>  	if (vec_count < 0)

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer