Currently we always keep the flow table maximally compact: that is all the
active entries are contiguous at the start of the table. Doing this
sometimes requires moving an entry when one is freed. That's kind of
fiddly, and potentially expensive: it requires updating the hash table for
the new location, and depending on flow type, it may require EPOLL_CTL_MOD,
system calls to update epoll tags with the new location too.
Implement a new way of managing the flow table that doesn't ever move
entries. It attempts to maintain some compactness by always using the
first free slot for a new connection, and mitigates the effect of non
compactness by cheaply skipping over contiguous blocks of free entries.
See the "theory of operation" comment in flow.c for details.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>b
[sbrivio: additional ASSERT(flow_first_free <= FLOW_MAX - 2) to avoid
Coverity Scan false positive]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Currently, flows are only evern finally freed (and the table compacted)
from the deferred handlers. Some future ways we want to optimise managing
the flow table will rely on this, so enforce it: rather than having the
TCP code directly call flow_table_compact(), add a boolean return value to
the per-flow deferred handlers. If true, this indicates that the flow
code itself should free the flow.
This forces all freeing of flows to occur during the flow code's scan of
the table in flow_defer_handler() which opens possibilities for future
optimisations.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Currently tcp.c open codes the process of allocating a new flow from the
flow table: twice, in fact, once for guest to host and once for host to
guest connections. This duplication isn't ideal and will get worse as we
add more protocols to the flow table. It also makes it harder to
experiment with different ways of handling flow table allocation.
Instead, introduce a function to allocate a new flow: flow_alloc(). In
some cases we currently check if we're able to allocate, but delay the
actual allocation. We now handle that slightly differently with a
flow_alloc_cancel() function to back out a recent allocation. We have that
separate from a flow_free() function, because future changes we have in
mind will need to handle this case a little differently.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
In general, the passt code is a bit haphazard about what's a true global
variable and what's in the quasi-global 'context structure'. The
flow_count field is one such example: it's in the context structure,
although it's really part of the same data structure as flowtab[], which
is a genuine global.
Move flow_count to be a regular global to match. For now it needs to be
public, rather than static, but we expect to be able to change that in
future.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
flow_log_() is a very basic widely used function that many other functions
in flow.c will end up needing. At present it's below flow_table_compact()
which happens not to need it, but that's likely to change. Move it to
near the top of flow.c to avoid forward declarations.
Code motion only, no changes.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
tcp_timer() scans the flow table so that it can run tcp_splice_timer() on
each spliced connection. More generally, other flow types might want to
run similar timers in future.
We could add a flow_timer() analagous to tcp_timer(), udp_timer() etc.
However, this would need to scan the flow table, which we would have just
done in flow_defer_handler(). We'd prefer to just scan the flow table
once, dispatching both per-flow deferred events and per-flow timed events
if necessary.
So, extend flow_defer_handler() to do this. For now we use the same timer
interval for all flow types (1s). We can make that more flexible in future
if we need to.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
tcp_defer_handler(), amongst other things, scans the flow table and does
some processing for each TCP connection. When we add other protocols to
the flow table, they're likely to want some similar scanning. It makes
more sense for cache friendliness to perform a single scan of the flow
table and dispatch to the protocol specific handlers, rather than having
each protocol separately scan the table.
To that end, add a new flow_defer_handler() handling all flow-linked
deferred operations.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
flow_table.h, the lower level flow header relies on having the struct
definitions for every protocol specific flow type - so far that means
tcp_conn.h. It doesn't include it itself, so tcp_conn.h must be included
before flow_table.h.
That's ok for now, but as we use the flow table for more things,
flow_table.h will need the structs for all of them, which means the
protocol specific .c files would need to include tcp_conn.h _and_ the
equivalents for every other flow type before flow_table.h every time,
which is weird.
So, although we *mostly* lean towards the include style where .c files need
to handle the include dependencies, in this case it makes more sense to
have flow_table.h include all the protocol specific headers it needs.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Most of the messages logged by the TCP code (be they errors, debug or
trace messages) are related to a specific connection / flow. We're fairly
consistent about prefixing these with the type of connection and the
connection / flow index. However there are a few places where we put the
index later in the message or omit it entirely. The template with the
prefix is also a little bulky to carry around for every message,
particularly for spliced connections.
To help keep this consistent, introduce some helpers to log messages
linked to a specific flow. It takes the flow as a parameter and adds a
uniform prefix to each message. This makes things slightly neater now, but
more importantly will help keep formatting consistent as we add more things
to the flow table.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
tcp_table_compact() will move entries in the connection/flow table to keep
it compact when other entries are removed. The moved entries need not have
the same type as the flow removed, so it needs to be able to handle moving
any type of flow. Therefore, move it to flow.c rather than being
purportedly TCP specific.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
We want to generalise "connection" tracking to things other than true TCP
connections. Continue implenenting this by renaming the TCP connection
table to the "flow table" and moving it to flow.c. The definitions are
split between flow.h and flow_table.h - we need this separation to avoid
circular dependencies: the definitions in flow.h will be needed by many
headers using the flow mechanism, but flow_table.h needs all those protocol
specific headers in order to define the full flow table entry.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Currently TCP connections use a 1-bit selector, 'spliced', to determine the
rest of the contents of the structure. We want to generalise the TCP
connection table to other types of flows in other protocols. Make a start
on this by replacing the tcp_conn_common structure with a new flow_common
structure with an enum rather than a simple boolean indicating the type of
flow.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
