genode/repos/os/include/block/component.h
Norman Feske bbe3ee8dc5 block_session: server-defined payload alignment
This patch replaces the formerly fixed 2 KiB data alignment within the
packet-stream buffer by a server-defined alignment. This has two
benefits.

First, when using block servers that provide small block sizes like 512
bytes, we avoid fragmenting the packet-stream buffer, which occurs when
aligning 512-byte requests at 2 KiB boundaries. This reduces meta data
costs for the packet-stream allocator and also allows fitting more
requests into the buffer.

Second, block drivers with alignment constraints dictated by the
hardware can now pass those constraints to the client, thereby easing
the use of zero-copy DMA directly into the packet stream.

The alignment is determined by the Block::Session_client at construction
time and applied by the Block::Session_client::alloc_packet method.
Block-session clients should always use this method, not the 'alloc_packet'
method of the packet stream (tx source) directly. The latter merely
applies a default alignment of 2 KiB.

At the server side, the alignment is automatically checked by
block/component.h (old API) and block/request_stream.h (new API).

Issue #3274
2019-05-03 13:53:12 +02:00

326 lines
9.2 KiB
C++

/*
* \brief Block-session component
* \author Christian Helmuth
* \author Stefan Kalkowski
* \date 2011-05-20
*/
/*
* Copyright (C) 2011-2017 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU Affero General Public License version 3.
*/
#ifndef _INCLUDE__BLOCK__COMPONENT_H_
#define _INCLUDE__BLOCK__COMPONENT_H_
#include <base/log.h>
#include <base/component.h>
#include <base/allocator_avl.h>
#include <base/heap.h>
#include <root/component.h>
#include <block/driver.h>
namespace Block {
using namespace Genode;
class Session_component_base;
class Session_component;
class Root;
};
/**
* We have a hen and egg situation that makes this base class necessary.
* The Block::Session_rpc_object construction depends on a dataspace for
* the packet stream. The dataspace on the other hand is constructed by
* the driver, which is created on demand when creating a session.
* When creating the driver, and dataspace outside the Session_component
* constructor within _create_session of the root component, we would have
* to destroy the driver and dataspace within the destructor body of
* Session_component, which will lead to problems, because the packet stream
* destructors will be called after the shared memory already vanished.
*/
class Block::Session_component_base
{
protected:
Driver_factory &_driver_factory;
Driver &_driver;
Ram_dataspace_capability _rq_ds;
Session_component_base(Driver_factory &factory, size_t tx_buf_size)
: _driver_factory(factory),
_driver(*factory.create()),
_rq_ds(_driver.alloc_dma_buffer(tx_buf_size)) {}
~Session_component_base()
{
_driver.free_dma_buffer(_rq_ds);
_driver_factory.destroy(&_driver);
}
};
class Block::Session_component : public Block::Session_component_base,
public Block::Driver_session
{
private:
addr_t _rq_phys;
Signal_handler<Session_component> _sink_ack;
Signal_handler<Session_component> _sink_submit;
bool _req_queue_full = false;
bool _ack_queue_full = false;
Packet_descriptor _p_to_handle { };
unsigned _p_in_fly;
Info const _info { _driver.info() };
bool const _writeable;
/**
* Acknowledge a packet already handled
*/
inline void _ack_packet(Packet_descriptor &packet)
{
if (!tx_sink()->ready_to_ack())
error("not ready to ack!");
tx_sink()->acknowledge_packet(packet);
_p_in_fly--;
}
/**
* Range check packet request
*/
inline bool _range_check(Packet_descriptor &p) {
return p.block_number() + p.block_count() - 1
< _info.block_count; }
/**
* Handle a single request
*/
void _handle_packet(Packet_descriptor packet)
{
_p_to_handle = packet;
_p_to_handle.succeeded(false);
/* ignore invalid packets */
bool const valid = packet.size() && _range_check(_p_to_handle)
&& tx_sink()->packet_valid(packet)
&& aligned(packet.offset(), _info.align_log2);
if (!valid) {
_ack_packet(_p_to_handle);
return;
}
try {
switch (_p_to_handle.operation()) {
case Block::Packet_descriptor::READ:
if (_driver.dma_enabled())
_driver.read_dma(packet.block_number(),
packet.block_count(),
_rq_phys + packet.offset(),
_p_to_handle);
else
_driver.read(packet.block_number(),
packet.block_count(),
tx_sink()->packet_content(packet),
_p_to_handle);
break;
case Block::Packet_descriptor::WRITE:
if (!_writeable) {
_ack_packet(_p_to_handle);
break;
}
if (_driver.dma_enabled())
_driver.write_dma(packet.block_number(),
packet.block_count(),
_rq_phys + packet.offset(),
_p_to_handle);
else
_driver.write(packet.block_number(),
packet.block_count(),
tx_sink()->packet_content(packet),
_p_to_handle);
break;
default:
throw Driver::Io_error();
}
} catch (Driver::Request_congestion) {
_req_queue_full = true;
} catch (Driver::Io_error) {
_ack_packet(_p_to_handle);
} catch (Genode::Packet_descriptor::Invalid_packet) {
_p_to_handle = Packet_descriptor();
Genode::error("dropping invalid Block packet");
}
}
/**
* Called whenever a signal from the packet-stream interface triggered
*/
void _signal()
{
/*
* as long as more packets are available, and we're able to ack
* them, and the driver's request queue isn't full,
* direct the packet request to the driver backend
*/
for (_ack_queue_full = (_p_in_fly >= tx_sink()->ack_slots_free());
!_req_queue_full && !_ack_queue_full
&& tx_sink()->packet_avail();
_ack_queue_full = (++_p_in_fly >= tx_sink()->ack_slots_free()))
_handle_packet(tx_sink()->get_packet());
}
public:
/**
* Constructor
*
* \param driver_factory factory to create and destroy driver objects
* \param ep entrypoint handling this session component
* \param buf_size size of packet-stream payload buffer
*/
Session_component(Driver_factory &driver_factory,
Genode::Entrypoint &ep,
Genode::Region_map &rm,
size_t buf_size,
bool writeable)
: Session_component_base(driver_factory, buf_size),
Driver_session(rm, _rq_ds, ep.rpc_ep()),
_rq_phys(Dataspace_client(_rq_ds).phys_addr()),
_sink_ack(ep, *this, &Session_component::_signal),
_sink_submit(ep, *this, &Session_component::_signal),
_req_queue_full(false),
_p_in_fly(0),
_writeable(writeable && _info.writeable)
{
_tx.sigh_ready_to_ack(_sink_ack);
_tx.sigh_packet_avail(_sink_submit);
_driver.session(this);
}
~Session_component() { _driver.session(nullptr); }
/**
* Acknowledges a packet processed by the driver to the client
*
* \param packet the packet to acknowledge
* \param success indicated whether the processing was successful
*
* \throw Ack_congestion
*/
void ack_packet(Packet_descriptor &packet, bool success) override
{
packet.succeeded(success);
_ack_packet(packet);
if (!_req_queue_full && !_ack_queue_full)
return;
/*
* when the driver's request queue was full,
* handle last unprocessed packet taken out of submit queue
*/
if (_req_queue_full) {
_req_queue_full = false;
_handle_packet(_p_to_handle);
}
/* resume packet processing */
_signal();
}
/*******************************
** Block session interface **
*******************************/
Info info() const override { return _driver.info(); }
void sync() override { _driver.sync(); }
};
/**
* Root component, handling new session requests
*/
class Block::Root : public Genode::Root_component<Block::Session_component,
Single_client>
{
private:
Driver_factory &_driver_factory;
Genode::Entrypoint &_ep;
Genode::Region_map &_rm;
bool const _writeable;
protected:
/**
* Always returns the singleton block-session component
*/
Session_component *_create_session(const char *args) override
{
size_t ram_quota =
Arg_string::find_arg(args, "ram_quota" ).ulong_value(0);
size_t tx_buf_size =
Arg_string::find_arg(args, "tx_buf_size").ulong_value(0);
/* delete ram quota by the memory needed for the session */
size_t session_size = max((size_t)4096,
sizeof(Session_component)
+ sizeof(Allocator_avl));
if (ram_quota < session_size)
throw Insufficient_ram_quota();
/*
* Check if donated ram quota suffices for both
* communication buffers. Also check both sizes separately
* to handle a possible overflow of the sum of both sizes.
*/
if (tx_buf_size > ram_quota - session_size) {
error("insufficient 'ram_quota', got ", ram_quota, ", need ",
tx_buf_size + session_size);
throw Insufficient_ram_quota();
}
bool writeable = _writeable
? Arg_string::find_arg(args, "writeable").bool_value(true)
: false;
return new (md_alloc()) Session_component(_driver_factory,
_ep, _rm, tx_buf_size,
writeable);
}
public:
/**
* Constructor
*
* \param ep entrypoint handling this root component
* \param md_alloc allocator to allocate session components
* \param rm region map
* \param driver_factory factory to create and destroy driver backend
*/
Root(Genode::Entrypoint &ep,
Allocator &md_alloc,
Genode::Region_map &rm,
Driver_factory &driver_factory,
bool writeable)
:
Root_component(ep, md_alloc),
_driver_factory(driver_factory), _ep(ep), _rm(rm), _writeable(writeable)
{ }
};
#endif /* _INCLUDE__BLOCK__COMPONENT_H_ */