[RFC PATCH v5 0/2] allocate multiple skbuffs on tx

[Arseniy Krasnov <avkrasnov@sberdevices.ru>]

This adds small optimization for tx path: instead of allocating single
skbuff on every call to transport, allocate multiple skbuff's until
credit space allows, thus trying to send as much as possible data without
return to af_vsock.c.

Also this patchset includes second patch which adds check and return from
'virtio_transport_get_credit()' and 'virtio_transport_put_credit()' when
these functions are called with 0 argument. This is needed, because zero
argument makes both functions to behave as no-effect, but both of them
always tries to acquire spinlock. Moreover, first patch always calls
function 'virtio_transport_put_credit()' with zero argument in case of
successful packet transmission.

 Link to v1:
 https://lore.kernel.org/netdev/2c52aa26-8181-d37a-bccd-a86bd3cbc6e1@sberdevices.ru/
 Link to v2:
 https://lore.kernel.org/netdev/ea5725eb-6cb5-cf15-2938-34e335a442fa@sberdevices.ru/
 Link to v3:
 https://lore.kernel.org/netdev/f33ef593-982e-2b3f-0986-6d537a3aaf08@sberdevices.ru/
 Link to v4:
 https://lore.kernel.org/netdev/0e0c1421-7cdc-2582-b120-cad6f42824bb@sberdevices.ru/

 Changelog:
 v1 -> v2:
 - If sent something, return number of bytes sent (even in
   case of error). Return error only if failed to sent first
   skbuff.

 v2 -> v3:
 - Handle case when transport callback returns unexpected value which
   is not equal to 'skb->len'. Break loop.
 - Don't check for zero value of 'rest_len' before calling
   'virtio_transport_put_credit()'. Decided to add this check directly
   to 'virtio_transport_put_credit()' in separate patch.

 v3 -> v4:
 - Use WARN_ONCE() to handle case when transport callback returns
   unexpected value.
 - Remove useless 'ret = -EFAULT;' assignment for case above.

 v4 -> v5:
 - Remove extra 'ret' initialization.
 - Remove empty extra line before 'if (ret < 0)'.
 - Add R-b tag for the first patch.
 - Add second patch, thus creating patchset of 2 patches.

Arseniy Krasnov (2):
  virtio/vsock: allocate multiple skbuffs on tx
  virtio/vsock: check argument to avoid no effect call

 net/vmw_vsock/virtio_transport_common.c | 63 +++++++++++++++++++------
 1 file changed, 49 insertions(+), 14 deletions(-)

-- 
2.25.1