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

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Thu, Jan 21, 2021 at 06:11:30PM +0100, Jesper Dangaard Brouer wrote:
> 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)

Please mention in commit message *how* you are addressing/fixing this
issue.

> > 
> > 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?

+1 on that question

> 
> 
> >  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
>