Re: [RFC PATCH v3 0/9] vsock: updates for SO_RCVLOWAT handling

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi Arseniy,
sorry but I didn't have time to review this series. I will definitely do it next Monday!

Have a nice weekend,
Stefano

On Wed, Aug 03, 2022 at 01:48:06PM +0000, Arseniy Krasnov wrote:
Hello,

This patchset includes some updates for SO_RCVLOWAT:

1) af_vsock:
  During my experiments with zerocopy receive, i found, that in some
  cases, poll() implementation violates POSIX: when socket has non-
  default SO_RCVLOWAT(e.g. not 1), poll() will always set POLLIN and
  POLLRDNORM bits in 'revents' even number of bytes available to read
  on socket is smaller than SO_RCVLOWAT value. In this case,user sees
  POLLIN flag and then tries to read data(for example using  'read()'
  call), but read call will be blocked, because  SO_RCVLOWAT logic is
  supported in dequeue loop in af_vsock.c. But the same time,  POSIX
  requires that:

  "POLLIN     Data other than high-priority data may be read without
              blocking.
   POLLRDNORM Normal data may be read without blocking."

  See https://www.open-std.org/jtc1/sc22/open/n4217.pdf, page 293.

  So, we have, that poll() syscall returns POLLIN, but read call will
  be blocked.

  Also in man page socket(7) i found that:

  "Since Linux 2.6.28, select(2), poll(2), and epoll(7) indicate a
  socket as readable only if at least SO_RCVLOWAT bytes are available."

  I checked TCP callback for poll()(net/ipv4/tcp.c, tcp_poll()), it
  uses SO_RCVLOWAT value to set POLLIN bit, also i've tested TCP with
  this case for TCP socket, it works as POSIX required.

  I've added some fixes to af_vsock.c and virtio_transport_common.c,
  test is also implemented.

2) virtio/vsock:
  It adds some optimization to wake ups, when new data arrived. Now,
  SO_RCVLOWAT is considered before wake up sleepers who wait new data.
  There is no sense, to kick waiter, when number of available bytes
  in socket's queue < SO_RCVLOWAT, because if we wake up reader in
  this case, it will wait for SO_RCVLOWAT data anyway during dequeue,
  or in poll() case, POLLIN/POLLRDNORM bits won't be set, so such
  exit from poll() will be "spurious". This logic is also used in TCP
  sockets.

3) vmci/vsock:
  Same as 2), but i'm not sure about this changes. Will be very good,
  to get comments from someone who knows this code.

4) Hyper-V:
  As Dexuan Cui mentioned, for Hyper-V transport it is difficult to
  support SO_RCVLOWAT, so he suggested to disable this feature for
  Hyper-V.

Thank You

Arseniy Krasnov(9):
vsock: SO_RCVLOWAT transport set callback
hv_sock: disable SO_RCVLOWAT support
virtio/vsock: use 'target' in notify_poll_in callback
vmci/vsock: use 'target' in notify_poll_in callback
vsock: pass sock_rcvlowat to notify_poll_in as target
vsock: add API call for data ready
virtio/vsock: check SO_RCVLOWAT before wake up reader
vmci/vsock: check SO_RCVLOWAT before wake up reader
vsock_test: POLLIN + SO_RCVLOWAT test

include/net/af_vsock.h                       |   2 +
net/vmw_vsock/af_vsock.c                     |  38 +++++++++-
net/vmw_vsock/hyperv_transport.c             |   7 ++
net/vmw_vsock/virtio_transport_common.c      |   7 +-
net/vmw_vsock/vmci_transport_notify.c        |  10 +--
net/vmw_vsock/vmci_transport_notify_qstate.c |  12 +--
tools/testing/vsock/vsock_test.c             | 107 +++++++++++++++++++++++++++
7 files changed, 166 insertions(+), 17 deletions(-)

Changelog:

v1 -> v2:
1) Patches for VMCI transport(same as for virtio-vsock).
2) Patches for Hyper-V transport(disabling SO_RCVLOWAT setting).
3) Waiting logic in test was updated(sleep() -> poll()).

v2 -> v3:
1) Patches were reordered.
2) Commit message updated in 0005.
3) Check 'transport' pointer in 0001 for NULL.
4) Check 'value' in 0001 for > buffer_size.

--
2.25.1




[Index of Archives]     [Linux Samsung SoC]     [Linux Rockchip SoC]     [Linux Actions SoC]     [Linux for Synopsys ARC Processors]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]


  Powered by Linux