kernel/linux.git/include/uapi/linux/tcp.h, branch linux-5.11.y

net-zerocopy: Defer vm zap unless actually needed.

2020-12-04T21:40:53+00:00

Zapping pages is required only if we are calling vm_insert_page into a region where pages had previously been mapped. Receive zerocopy allows reusing such regions, and hitherto called zap_page_range() before calling vm_insert_page() in that range. zap_page_range() can also be triggered from userspace with madvise(MADV_DONTNEED). If userspace is configured to call this before reusing a segment, or if there was nothing mapped at this virtual address to begin with, we can avoid calling zap_page_range() under the socket lock. That said, if userspace does not do that, then we are still responsible for calling zap_page_range(). This patch adds a flag that the user can use to hint to the kernel that a zap is not required. If the flag is not set, or if an older user application does not have a flags field at all, then the kernel calls zap_page_range as before. Also, if the flag is set but a zap is still required, the kernel performs that zap as necessary. Thus incorrectly indicating that a zap can be avoided does not change the correctness of operation. It also increases the batchsize for vm_insert_pages and prefetches the page struct for the batch since we're about to bump the refcount. An alternative mechanism could be to not have a flag, assume by default a zap is not needed, and fall back to zapping if needed. However, this would harm performance for older applications for which a zap is necessary, and thus we implement it with an explicit flag so newer applications can opt in. When using RPC-style traffic with medium sized (tens of KB) RPCs, this change yields an efficency improvement of about 30% for QPS/CPU usage. Signed-off-by: Arjun Roy Signed-off-by: Eric Dumazet Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: Jakub Kicinski

net-zerocopy: Copy straggler unaligned data for TCP Rx. zerocopy.

2020-12-04T21:40:52+00:00

When TCP receive zerocopy does not successfully map the entire requested space, it outputs a 'hint' that the caller should recvmsg(). Augment zerocopy to accept a user buffer that it tries to copy this hint into - if it is possible to copy the entire hint, it will do so. This elides a recvmsg() call for received traffic that isn't exactly page-aligned in size. This was tested with RPC-style traffic of arbitrary sizes. Normally, each received message required at least one getsockopt() call, and one recvmsg() call for the remaining unaligned data. With this change, almost all of the recvmsg() calls are eliminated, leading to a savings of about 25%-50% in number of system calls for RPC-style workloads. Signed-off-by: Arjun Roy Signed-off-by: Eric Dumazet Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: Jakub Kicinski

tcp: add earliest departure time to SCM_TIMESTAMPING_OPT_STATS

2020-08-01T00:00:44+00:00

This change adds TCP_NLA_EDT to SCM_TIMESTAMPING_OPT_STATS that reports the earliest departure time(EDT) of the timestamped skb. By tracking EDT values of the skb from different timestamps, we can observe when and how much the value changed. This allows to measure the precise delay injected on the sender host e.g. by a bpf-base throttler. Signed-off-by: Yousuk Seung Signed-off-by: Eric Dumazet Acked-by: Neal Cardwell Acked-by: Soheil Hassas Yeganeh Acked-by: Yuchung Cheng Signed-off-by: David S. Miller

tcp: add bytes not sent to SCM_TIMESTAMPING_OPT_STATS

2020-03-10T00:56:33+00:00

Add TCP_NLA_BYTES_NOTSENT to SCM_TIMESTAMPING_OPT_STATS that reports bytes in the write queue but not sent. This is the same metric as what is exported with tcp_info.tcpi_notsent_bytes. Signed-off-by: Yousuk Seung Signed-off-by: Eric Dumazet Acked-by: Soheil Hassas Yeganeh Acked-by: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller

tcp-zerocopy: Return sk_err (if set) along with tcp receive zerocopy.

2020-02-17T03:25:02+00:00

This patchset is intended to reduce the number of extra system calls imposed by TCP receive zerocopy. For ping-pong RPC style workloads, this patchset has demonstrated a system call reduction of about 30% when coupled with userspace changes. For applications using epoll, returning sk_err along with the result of tcp receive zerocopy could remove the need to call recvmsg()=-EAGAIN after a spurious wakeup. Consider a multi-threaded application using epoll. A thread may awaken with EPOLLIN but another thread may already be reading. The spuriously-awoken thread does not necessarily know that another thread 'won'; rather, it may be possible that it was woken up due to the presence of an error if there is no data. A zerocopy read receiving 0 bytes thus would need to be followed up by recvmsg to be sure. Instead, we return sk_err directly with zerocopy, so the application can avoid this extra system call. Signed-off-by: Arjun Roy Signed-off-by: Eric Dumazet Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller

tcp-zerocopy: Return inq along with tcp receive zerocopy.

2020-02-17T03:25:02+00:00

This patchset is intended to reduce the number of extra system calls imposed by TCP receive zerocopy. For ping-pong RPC style workloads, this patchset has demonstrated a system call reduction of about 30% when coupled with userspace changes. For applications using edge-triggered epoll, returning inq along with the result of tcp receive zerocopy could remove the need to call recvmsg()=-EAGAIN after a successful zerocopy. Generally speaking, since normally we would need to perform a recvmsg() call for every successful small RPC read via TCP receive zerocopy, returning inq can reduce the number of system calls performed by approximately half. Signed-off-by: Arjun Roy Signed-off-by: Eric Dumazet Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller

tcp: export count for rehash attempts

2020-01-26T14:28:47+00:00

Using IPv6 flow-label to swiftly route around avoid congested or disconnected network path can greatly improve TCP reliability. This patch adds SNMP counters and a OPT_STATS counter to track both host-level and connection-level statistics. Network administrators can use these counters to evaluate the impact of this new ability better. Export count for rehash attempts to 1) two SNMP counters: TcpTimeoutRehash (rehash due to timeouts), and TcpDuplicateDataRehash (rehash due to receiving duplicate packets) 2) Timestamping API SOF_TIMESTAMPING_OPT_STATS. Signed-off-by: Abdul Kabbani Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Kevin(Yudong) Yang Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

net: Add device index to tcp_md5sig

2020-01-02T23:51:22+00:00

Add support for userspace to specify a device index to limit the scope of an entry via the TCP_MD5SIG_EXT setsockopt. The existing __tcpm_pad is renamed to tcpm_ifindex and the new field is only checked if the new TCP_MD5SIG_FLAG_IFINDEX is set in tcpm_flags. For now, the device index must point to an L3 master device (e.g., VRF). The API and error handling are setup to allow the constraint to be relaxed in the future to any device index. Signed-off-by: David Ahern Signed-off-by: David S. Miller

tcp: add TCP_INFO status for failed client TFO

2019-10-26T02:25:37+00:00

The TCPI_OPT_SYN_DATA bit as part of tcpi_options currently reports whether or not data-in-SYN was ack'd on both the client and server side. We'd like to gather more information on the client-side in the failure case in order to indicate the reason for the failure. This can be useful for not only debugging TFO, but also for creating TFO socket policies. For example, if a middle box removes the TFO option or drops a data-in-SYN, we can can detect this case, and turn off TFO for these connections saving the extra retransmits. The newly added tcpi_fastopen_client_fail status is 2 bits and has the following 4 states: 1) TFO_STATUS_UNSPEC Catch-all state which includes when TFO is disabled via black hole detection, which is indicated via LINUX_MIB_TCPFASTOPENBLACKHOLE. 2) TFO_COOKIE_UNAVAILABLE If TFO_CLIENT_NO_COOKIE mode is off, this state indicates that no cookie is available in the cache. 3) TFO_DATA_NOT_ACKED Data was sent with SYN, we received a SYN/ACK but it did not cover the data portion. Cookie is not accepted by server because the cookie may be invalid or the server may be overloaded. 4) TFO_SYN_RETRANSMITTED Data was sent with SYN, we received a SYN/ACK which did not cover the data after at least 1 additional SYN was sent (without data). It may be the case that a middle-box is dropping data-in-SYN packets. Thus, it would be more efficient to not use TFO on this connection to avoid extra retransmits during connection establishment. These new fields do not cover all the cases where TFO may fail, but other failures, such as SYN/ACK + data being dropped, will result in the connection not becoming established. And a connection blackhole after session establishment shows up as a stalled connection. Signed-off-by: Jason Baron Cc: Eric Dumazet Cc: Neal Cardwell Cc: Christoph Paasch Cc: Yuchung Cheng Acked-by: Yuchung Cheng Signed-off-by: David S. Miller

tcp: Add snd_wnd to TCP_INFO

2019-09-16T14:26:11+00:00

Neal Cardwell mentioned that snd_wnd would be useful for diagnosing TCP performance problems -- > (1) Usually when we're diagnosing TCP performance problems, we do so > from the sender, since the sender makes most of the > performance-critical decisions (cwnd, pacing, TSO size, TSQ, etc). > From the sender-side the thing that would be most useful is to see > tp->snd_wnd, the receive window that the receiver has advertised to > the sender. This serves the purpose of adding an additional __u32 to avoid the would-be hole caused by the addition of the tcpi_rcvi_ooopack field. Signed-off-by: Thomas Higdon Acked-by: Yuchung Cheng Acked-by: Neal Cardwell Acked-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller