Inheritance diagram for TableLayout:

[legend]

Public Member Functions
	TableLayout (PhvInfo &p, LayoutChoices &l, SplitAttachedInfo &sia)

Public Member Functions inherited from P4::PassManager
	PassManager (const PassManager &)=default

	PassManager (const std::initializer_list< VisitorRef > &init)

	PassManager (PassManager &&)=default

void	addDebugHook (DebugHook h, bool recursive=false)

void	addDebugHooks (std::vector< DebugHook > hooks, bool recursive=false)

void	addPasses (const std::initializer_list< VisitorRef > &init)

const IR::Node *	apply_visitor (const IR::Node , const char =0) override

bool	backtrack (trigger &trig) override

PassManager *	clone () const override

void	early_exit ()

void	listPasses (std::ostream &, cstring sep) const

bool	never_backtracks () override

void	removePasses (const std::vector< cstring > &exclude)

void	setStopOnError (bool stop)

Public Member Functions inherited from P4::Visitor
virtual bool	check_clone (const Visitor *a)

virtual bool	check_global (cstring)

virtual void	clear_globals ()

virtual ControlFlowVisitor *	controlFlowVisitor ()

virtual void	end_apply ()

virtual void	end_apply (const IR::Node *root)

virtual void	erase_global (cstring)

template<class T >
const T *	findContext () const

template<class T >
const T *	findContext (const Context *&c) const

template<class T >
const T *	findOrigCtxt () const

template<class T >
const T *	findOrigCtxt (const Context *&c) const

virtual Visitor &	flow_clone ()

virtual void	flow_merge (Visitor &)

virtual bool	flow_merge_closure (Visitor &)

virtual void	flow_merge_global_from (cstring)

virtual void	flow_merge_global_to (cstring)

const Context *	getChildContext () const

int	getChildrenVisited () const

const Context *	getContext () const

int	getContextDepth () const

const IR::Node *	getCurrentNode () const

template<class T >
const T *	getCurrentNode () const

const IR::Node *	getOriginal () const

template<class T >
const T *	getOriginal () const

template<class T >
const T *	getParent () const

virtual bool	has_flow_joins () const

profile_t	init_apply (const IR::Node root, const Context parent_context)

bool	isInContext (const IR::Node *n) const

virtual const char *	name () const

template<class T >
void	parallel_visit (const IR::Vector< T > &v, const char *name, int cidx)

template<class T >
void	parallel_visit (const IR::Vector< T > &v, const char *name=0)

template<class T >
void	parallel_visit (IR::Vector< T > &v, const char *name, int cidx)

template<class T >
void	parallel_visit (IR::Vector< T > &v, const char *name=0)

void	print_context () const

const Visitor &	setCalledBy (const Visitor *visitor)

void	setName (const char *name)

void	visit (const IR::Node &n, const char *name, int cidx)

void	visit (const IR::Node &n, const char *name=0)

void	visit (const IR::Node &n, const char name, int cidx)

void	visit (const IR::Node &n, const char name=0)

void	visit (const IR::Node const &n, const char name, int cidx)

void	visit (const IR::Node const &n, const char name=0)

void	visit (IR::Node &n, const char *name, int cidx)

void	visit (IR::Node &n, const char *name=0)

void	visit (IR::Node &, const char =0, int=0)

template<class T , typename = std::enable_if_t<Util::has_SourceInfo_v<T> && !std::is_pointer_v<T>>, class... Args>
void	warn (const int kind, const char *format, const T &node, Args &&...args)
	The const ref variant of the above.

template<class T , typename = std::enable_if_t<Util::has_SourceInfo_v<T>>, class... Args>
void	warn (const int kind, const char format, const T node, Args &&...args)

bool	warning_enabled (int warning_kind) const

Public Member Functions inherited from P4::Backtrack

Static Public Member Functions
static void	check_for_alpm (IR::MAU::Table::Layout &, const IR::MAU::Table *tbl, cstring &partition_index, const PhvInfo &phv)

static void	check_for_atcam (IR::MAU::Table::Layout &layout, const IR::MAU::Table *tbl, cstring &partition_index, const PhvInfo &phv)

static void	check_for_ternary (IR::MAU::Table::Layout &layout, const IR::MAU::Table *tbl)

Static Public Member Functions inherited from P4::Visitor
static cstring	demangle (const char *)

static bool	warning_enabled (const Visitor *visitor, int warning_kind)

Additional Inherited Members
Public Types inherited from P4::Visitor
typedef Visitor_Context	Context

Public Attributes inherited from P4::Visitor
const Visitor *	called_by = nullptr

cstring	internalName

SplitFlowVisit_base *&	split_link

SplitFlowVisit_base *	split_link_mem = nullptr

Protected Member Functions inherited from P4::PassManager
profile_t	init_apply (const IR::Node *root) override

void	runDebugHooks (const char visitorName, const IR::Node node)

Protected Member Functions inherited from P4::Visitor
virtual void	init_join_flows (const IR::Node *)

virtual bool	join_flows (const IR::Node *)

virtual void	post_join_flows (const IR::Node , const IR::Node )

void	visit_children (const IR::Node *, std::function< void()> fn)

virtual void	visitAgain () const

virtual void	visitOnce () const

Protected Attributes inherited from P4::PassManager
safe_vector< DebugHook >	debugHooks

safe_vector< Visitor * >	passes

bool	running = false

unsigned	seqNo = 0

bool	stop_on_error = true

Protected Attributes inherited from P4::Visitor
bool	dontForwardChildrenBeforePreorder = false

bool	joinFlows = false

bool	visitDagOnce = true

Member Function Documentation

◆ check_for_atcam()

void TableLayout::check_for_atcam	(	IR::MAU::Table::Layout &	layout,
		const IR::MAU::Table *	tbl,
		cstring &	partition_index,
		const PhvInfo &	phv )

static

Algorithmic TCAM is a third type of table, in the same vein as ternary and exact. An ATCAM table is a ternary table that Tofino can implement using exact hardware, specifically the SRAM array.

A ternary match requires two things that a normal exact match cannot. A ternary match must be able to specify a don't care for any bit, and must have a priority system in order to rank the matches. By using particular features of the SRAM array, the Tofino target can create these features.

The don't care bit is possible due by containing any ternary match data twice in the RAM line. The match data is encoded to match as 0, 1, or don't care. This is briefly described in section 6.4.2.2 Algorithmic TCAM section of the Tofino uArch, while the encoding scheme for ternary match in general is described in section 6.3.1 TCAM Data Representation. The terms s0q1 and s1q0 describe these different encodings.

Priority is engineered through the placement of RAMs in a row. If the RAMs are in the same row, and belong to the same ATCAM table, then if multiple tables match, as is possible within a single TCAM table, the one closer to the edge of the chip will have higher priority and will be the match. If the algorithm cannot fit all of the entries within a single row, then the table will be split into multiple logical tables, and will use hit/miss predication of these logical tables in order to generate priority across tables. This is described by section 1.4.5 Algorithmic TCAM Overview in the uArch.

An ATCAM table requires a partition index. This is an field in the key that must be an exact match. This partition index is used as an identity hash to find the correct partition within the massive ATCAM table.

The user can also specify the number of partitions. In a standard TCAM, the size of the table specifies how many entries are looked up (logically) simultaneously. In an ATCAM table, the number of entries that are looked up simultaneously is: table_size / number_of_partitions

If no number of partitions is specified, then the number of partitions is: 2 ^ (partition index bits)

Public Member Functions

Static Public Member Functions

Additional Inherited Members

Member Function Documentation

◆ check_for_atcam()