Most of TCP stack assumed it was running from BH handler. This is great for most things, as TCP behavior is very sensitive to scheduling artifacts.
However, the prequeue and backlog processing are problematic, as they need to be flushed with BH being blocked. To cope with modern needs, TCP sockets have big sk_rcvbuf values, in the order of 16 MB. This means that backlog can hold thousands of packets, and things like TCP coalescing or collapsing on this amount of packets can lead to insane latency spikes, since BH are blocked for too long. It is time to make UDP/TCP stacks preemptible. Note that fast path still runs from BH handler. Eric Dumazet (6): tcp: do not assume TCP code is non preemptible tcp: do not block bh during prequeue processing dccp: do not assume DCCP code is non preemptible udp: prepare for non BH masking at backlog processing sctp: prepare for socket backlog behavior change net: do not block BH while processing socket backlog net/core/sock.c | 22 +++------ net/dccp/input.c | 2 +- net/dccp/ipv4.c | 4 +- net/dccp/ipv6.c | 4 +- net/dccp/options.c | 2 +- net/ipv4/tcp.c | 6 +-- net/ipv4/tcp_cdg.c | 20 ++++---- net/ipv4/tcp_cubic.c | 20 ++++---- net/ipv4/tcp_fastopen.c | 12 ++--- net/ipv4/tcp_input.c | 126 +++++++++++++++++++---------------------------- net/ipv4/tcp_ipv4.c | 14 ++++-- net/ipv4/tcp_minisocks.c | 2 +- net/ipv4/tcp_output.c | 7 ++- net/ipv4/tcp_recovery.c | 4 +- net/ipv4/tcp_timer.c | 10 ++-- net/ipv4/udp.c | 4 +- net/ipv6/tcp_ipv6.c | 12 ++--- net/ipv6/udp.c | 4 +- net/sctp/inqueue.c | 2 + 19 files changed, 124 insertions(+), 153 deletions(-) -- 2.8.0.rc3.226.g39d4020
