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

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Date:   Thu, 21 Jan 2021 18:11:30 +0100
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Ivan Babrou <ivan@...udflare.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, kernel-team@...udflare.com,
        Edward Cree <ecree.xilinx@...il.com>,
        Martin Habets <habetsm.xilinx@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH net-next] sfc: reduce the number of requested xdp ev
 queues

On Wed, 20 Jan 2021 13:27:59 -0800
Ivan Babrou <ivan@...udflare.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@...udflare.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