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Date: Fri, 28 Jun 2019 03:01:26 +0000 From: "Brown, Aaron F" <aaron.f.brown@...el.com> To: "Patel, Vedang" <vedang.patel@...el.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> CC: "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>, "davem@...emloft.net" <davem@...emloft.net>, "jhs@...atatu.com" <jhs@...atatu.com>, "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>, "jiri@...nulli.us" <jiri@...nulli.us>, "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>, "Gomes, Vinicius" <vinicius.gomes@...el.com>, "l@...ileo.org" <l@...ileo.org>, "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>, "m-karicheri2@...com" <m-karicheri2@...com>, "sergei.shtylyov@...entembedded.com" <sergei.shtylyov@...entembedded.com>, "eric.dumazet@...il.com" <eric.dumazet@...il.com> Subject: RE: [PATCH net-next v6 1/8] igb: clear out skb->tstamp after reading the txtime > From: Patel, Vedang > Sent: Tuesday, June 25, 2019 3:07 PM > To: netdev@...r.kernel.org > Cc: Kirsher, Jeffrey T <jeffrey.t.kirsher@...el.com>; davem@...emloft.net; > jhs@...atatu.com; xiyou.wangcong@...il.com; jiri@...nulli.us; intel-wired- > lan@...ts.osuosl.org; Gomes, Vinicius <vinicius.gomes@...el.com>; > l@...ileo.org; jakub.kicinski@...ronome.com; m-karicheri2@...com; > sergei.shtylyov@...entembedded.com; eric.dumazet@...il.com; Brown, > Aaron F <aaron.f.brown@...el.com>; Patel, Vedang <vedang.patel@...el.com> > Subject: [PATCH net-next v6 1/8] igb: clear out skb->tstamp after reading the > txtime > > If a packet which is utilizing the launchtime feature (via SO_TXTIME socket > option) also requests the hardware transmit timestamp, the hardware > timestamp is not delivered to the userspace. This is because the value in > skb->tstamp is mistaken as the software timestamp. > > Applications, like ptp4l, request a hardware timestamp by setting the > SOF_TIMESTAMPING_TX_HARDWARE socket option. Whenever a new > timestamp is > detected by the driver (this work is done in igb_ptp_tx_work() which calls > igb_ptp_tx_hwtstamps() in igb_ptp.c[1]), it will queue the timestamp in the > ERR_QUEUE for the userspace to read. When the userspace is ready, it will > issue a recvmsg() call to collect this timestamp. The problem is in this > recvmsg() call. If the skb->tstamp is not cleared out, it will be > interpreted as a software timestamp and the hardware tx timestamp will not > be successfully sent to the userspace. Look at skb_is_swtx_tstamp() and the > callee function __sock_recv_timestamp() in net/socket.c for more details. > > Signed-off-by: Vedang Patel <vedang.patel@...el.com> > --- > drivers/net/ethernet/intel/igb/igb_main.c | 1 + > 1 file changed, 1 insertion(+) > Tested-by: Aaron Brown <aaron.f.brown@...el.com>
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