From: Íñigo Huguet ihuguet@redhat.com
[ Upstream commit f28100cb9c9645c07cbd22431278ac9492f6a01c ]
Fixes: e26ca4b53582 sfc: reduce the number of requested xdp ev queues
The buggy commit intended to allocate less channels for XDP in order to be more unlikely to reach the limit of 32 channels of the driver.
The idea was to use each IRQ/eventqeue for more XDP TX queues than before, calculating which is the maximum number of TX queues that one event queue can handle. For example, in EF10 each event queue could handle up to 8 queues, better than the 4 they were handling before the change. This way, it would have to allocate half of channels than before for XDP TX.
The problem is that the TX queues are also contained inside the channel structs, and there are only 4 queues per channel. Reducing the number of channels means also reducing the number of queues, resulting in not having the desired number of 1 queue per CPU.
This leads to getting errors on XDP_TX and XDP_REDIRECT if they're executed from a high numbered CPU, because there only exist queues for the low half of CPUs, actually. If XDP_TX/REDIRECT is executed in a low numbered CPU, the error doesn't happen. This is the error in the logs (repeated many times, even rate limited): sfc 0000:5e:00.0 ens3f0np0: XDP TX failed (-22)
This errors happens in function efx_xdp_tx_buffers, where it expects to have a dedicated XDP TX queue per CPU.
Reverting the change makes again more likely to reach the limit of 32 channels in machines with many CPUs. If this happen, no XDP_TX/REDIRECT will be possible at all, and we will have this log error messages:
At interface probe: sfc 0000:5e:00.0: Insufficient resources for 12 XDP event queues (24 other channels, max 32)
At every subsequent XDP_TX/REDIRECT failure, rate limited: sfc 0000:5e:00.0 ens3f0np0: XDP TX failed (-22)
However, without reverting the change, it makes the user to think that everything is OK at probe time, but later it fails in an unpredictable way, depending on the CPU that handles the packet.
It is better to restore the predictable behaviour. If the user sees the error message at probe time, he/she can try to configure the best way it fits his/her needs. At least, he/she will have 2 options: - Accept that XDP_TX/REDIRECT is not available (he/she may not need it) - Load sfc module with modparam 'rss_cpus' with a lower number, thus creating less normal RX queues/channels, letting more free resources for XDP, with some performance penalty.
Anyway, let the calculation of maximum TX queues that can be handled by a single event queue, and use it only if it's less than the number of TX queues per channel. This doesn't happen in practice, but could happen if some constant values are tweaked in the future, such us EFX_MAX_TXQ_PER_CHANNEL, EFX_MAX_EVQ_SIZE or EFX_MAX_DMAQ_SIZE.
Related mailing list thread: https://lore.kernel.org/bpf/20201215104327.2be76156@carbon/
Signed-off-by: Íñigo Huguet ihuguet@redhat.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/ethernet/sfc/efx_channels.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/sfc/efx_channels.c b/drivers/net/ethernet/sfc/efx_channels.c index a3ca406a3561..5b71f8a03a6d 100644 --- a/drivers/net/ethernet/sfc/efx_channels.c +++ b/drivers/net/ethernet/sfc/efx_channels.c @@ -152,6 +152,7 @@ static int efx_allocate_msix_channels(struct efx_nic *efx, * maximum size. */ tx_per_ev = EFX_MAX_EVQ_SIZE / EFX_TXQ_MAX_ENT(efx); + tx_per_ev = min(tx_per_ev, EFX_MAX_TXQ_PER_CHANNEL); n_xdp_tx = num_possible_cpus(); n_xdp_ev = DIV_ROUND_UP(n_xdp_tx, tx_per_ev);
@@ -181,7 +182,7 @@ static int efx_allocate_msix_channels(struct efx_nic *efx, efx->xdp_tx_queue_count = 0; } else { efx->n_xdp_channels = n_xdp_ev; - efx->xdp_tx_per_channel = EFX_MAX_TXQ_PER_CHANNEL; + efx->xdp_tx_per_channel = tx_per_ev; efx->xdp_tx_queue_count = n_xdp_tx; n_channels += n_xdp_ev; netif_dbg(efx, drv, efx->net_dev,