On Thu, 13 Jun 2019 14:01:39 +0000, Maxim Mikityanskiy wrote: > On 2019-06-12 23:23, Jakub Kicinski wrote: > > On Wed, 12 Jun 2019 15:56:48 +0000, Maxim Mikityanskiy wrote: > >> Currently, libbpf uses the number of combined channels as the maximum > >> queue number. However, the kernel has a different limitation: > >> > >> - xdp_reg_umem_at_qid() allows up to max(RX queues, TX queues). > >> > >> - ethtool_set_channels() checks for UMEMs in queues up to > >> combined_count + max(rx_count, tx_count). > >> > >> libbpf shouldn't limit applications to a lower max queue number. Account > >> for non-combined RX and TX channels when calculating the max queue > >> number. Use the same formula that is used in ethtool. > >> > >> Signed-off-by: Maxim Mikityanskiy <maximmi@xxxxxxxxxxxx> > >> Reviewed-by: Tariq Toukan <tariqt@xxxxxxxxxxxx> > >> Acked-by: Saeed Mahameed <saeedm@xxxxxxxxxxxx> > > > > I don't think this is correct. max_tx tells you how many TX channels > > there can be, you can't add that to combined. Correct calculations is: > > > > max_num_chans = max(max_combined, max(max_rx, max_tx)) > > First of all, I'm aligning with the formula in the kernel, which is: > > curr.combined_count + max(curr.rx_count, curr.tx_count); > > (see net/core/ethtool.c, ethtool_set_channels()). curr != max. ethtool code you're pointing me to (and which I wrote) uses the current allocation, not the max values. > The formula in libbpf should match it. The formula should be based on understanding what we're doing, not copying some not-really-equivalent code from somewhere :) Combined is a basically a queue pair, RX is an RX ring with a dedicated IRQ, and TX is a TX ring with a dedicated IRQ. If driver supports both combined and single purpose interrupt vectors it will most likely set max_rx = num_hw_rx max_tx = num_hw_tx max_combined = min(rx, tx) Like with most ethtool APIs there are some variations to this. > Second, the existing drivers have either combined channels or separate > rx and tx channels. So, for the first kind of drivers, max_tx doesn't > tell how many TX channels there can be, it just says 0, and max_combined > tells how many TX and RX channels are supported. As max_tx doesn't > include max_combined (and vice versa), we should add them up. By existing drivers you mean Intel drivers which implement AF_XDP, and your driver? Both Intel and MLX drivers seem to only set max_combined. If you mean all drivers across the kernel, then I believe the best formula is what I gave you. > >> tools/lib/bpf/xsk.c | 6 +++--- > >> 1 file changed, 3 insertions(+), 3 deletions(-) > >> > >> diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c > >> index bf15a80a37c2..86107857e1f0 100644 > >> --- a/tools/lib/bpf/xsk.c > >> +++ b/tools/lib/bpf/xsk.c > >> @@ -334,13 +334,13 @@ static int xsk_get_max_queues(struct xsk_socket *xsk) > >> goto out; > >> } > >> > >> - if (channels.max_combined == 0 || errno == EOPNOTSUPP) > >> + ret = channels.max_combined + max(channels.max_rx, channels.max_tx); > >> + > >> + if (ret == 0 || errno == EOPNOTSUPP) > >> /* If the device says it has no channels, then all traffic > >> * is sent to a single stream, so max queues = 1. > >> */ > >> ret = 1; > >> - else > >> - ret = channels.max_combined; > >> > >> out: > >> close(fd);
