Hello Oliver, On 2015-06-21 00:42, Oliver Hartkopp wrote:
>> 514ac99c64b22d83b52dfee3b8becaa69a92bc4a introduces a frame equality >> check. Since the sk_buff pointer is not sufficient to do this (buffers >> are reused), the check also compares time stamps. >> In short: pointer+time stamp was assumed as unique key to a specific >> frame. >> The problem with this is, that the time stamp is an optional property >> and not set per default. >> In our case (flexcan) the time stamp is always zero, so the equality >> check is reduced to equality of buffer pointers, resulting in a lot of >> dropped frames. > > The question is why your system did not generate a timestamp at the time of > skb reception. > > Usually when netif_rx(), netif_rx_ni() is invoked the timestamp is set in the > following reception process. > > flexcan.c only uses netif_receive_skb() - but all theses functions set the > timestamp > > net_timestamp_check(netdev_tstamp_prequeue, skb); > > depending on netdev_tstamp_prequeue which is configured by > > /proc/sys/net/core/netdev_tstamp_prequeue > > See the idea of netdev_tstamp_prequeue here: > > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/net/core/sysctl_net_core.c?id=3b098e2d7c693796cc4dffb07caa249fc0f70771 > Thank you for the background information! I've also noticed your patch [PATCH - regression 4.1-rc8] can: fix loss of CAN frames in raw_rcv > Can you tell me the output of /proc/sys/net/core/netdev_tstamp_prequeue on > your machine? /proc/sys/net/core/netdev_tstamp_prequeue is set to 1 (unmodified, default) I tried to dig a little deeper in timestamping: 1. (net/core/dev.c) I found that static_key_false(&netstamp_needed) is always 0, resulting that the timestamp is never set by net_timestamp_check in netif_receive_skb_internal. 2. (net/core/dev.c) static_key_false(&netstamp_needed) is 0 because net_enable_timestamp is never called. 3. (net/core/sock.c) net_enable_timestamp is never called because SK_FLAGS_TIMESTAMP is not set 4. (net/core/sock.c) SK_FLAGS_TIMESTAMP is not set because neither of SOCK_TIMESTAMP or SOCK_TIMESTAMPING_RX_SOFTWARE is set 5. (net/core/sock.c) SOCK_TIMESTAMP or SOCK_TIMESTAMPING_RX_SOFTWARE is not set because timestamping is an optional feature (according to http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/networking/timestamping.txt?id=b953c0d234bc72e8489d3bf51a276c5c4ec85345) not enabled in my use case (even if netdev_tstamp_prequeue is set to 1) So the original assumption for the was correct: The correctness of the skb equality check depends on a feature that is not enabled by default (respectively user configurable). Do you agree with this? > > Thanks again for your investigation! Sure! Best regards, Manfred -- To unsubscribe from this list: send the line "unsubscribe netdev" in
