um: add shared memory optimisation for time-travel=ext

With external time travel, a LOT of message can end up
being exchanged on the socket, taking a significant
amount of time just to do that.

Add a new shared memory optimisation to that, where a
number of changes are made:
 - the controller sends a client ID and a shared memory FD
   (and a logging FD we don't use) in the ACK message to
   the initial START
 - the shared memory holds the current time and the
   free_until value, so that there's no need to exchange
   messages for that
 - if the client that's running has shared memory support,
   any client (the running one included) can request the
   next time it wants to run inside the shared memory,
   rather than sending a message, by also updating the
   free_until value
 - when shared memory is enabled, RUN/WAIT messages no
   longer have an ACK, further cutting down on messages

Together, this can reduce the number of messages very
significantly, and reduce overall test/simulation run time.

Co-developed-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Link: https://patch.msgid.link/20240702192118.6ad0a083f574.Ie41206c8ce4507fe26b991937f47e86c24ca7a31@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 165 insertions, 14 deletions

diff --git a/include/uapi/linux/um_timetravel.h b/include/uapi/linux/um_timetravel.h
index 078ea401aa2a..546a690b0346 100644
--- a/include/uapi/linux/um_timetravel.h
+++ b/include/uapi/linux/um_timetravel.h
@@ -1,17 +1,6 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
 /*
- * Permission to use, copy, modify, and/or distribute this software for any
- * purpose with or without fee is hereby granted, provided that the above
- * copyright notice and this permission notice appear in all copies.
- *
- * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
- * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
- * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
- * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
- * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
- * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
- * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
- *
- * Copyright (C) 2019 Intel Corporation
+ * Copyright (C) 2019 - 2023 Intel Corporation
  */
 #ifndef _UAPI_LINUX_UM_TIMETRAVEL_H
 #define _UAPI_LINUX_UM_TIMETRAVEL_H
@@ -50,6 +39,36 @@ struct um_timetravel_msg {
 	__u64 time;
 };
 
+/* max number of file descriptors that can be sent/received in a message */
+#define UM_TIMETRAVEL_MAX_FDS 2
+
+/**
+ * enum um_timetravel_shared_mem_fds - fds sent in ACK message for START message
+ */
+enum um_timetravel_shared_mem_fds {
+	/**
+	 * @UM_TIMETRAVEL_SHARED_MEMFD: Index of the shared memory file
+	 *	descriptor in the control message
+	 */
+	UM_TIMETRAVEL_SHARED_MEMFD,
+	/**
+	 * @UM_TIMETRAVEL_SHARED_LOGFD: Index of the logging file descriptor
+	 *	in the control message
+	 */
+	UM_TIMETRAVEL_SHARED_LOGFD,
+	UM_TIMETRAVEL_SHARED_MAX_FDS,
+};
+
+/**
+ * enum um_timetravel_start_ack - ack-time mask for start message
+ */
+enum um_timetravel_start_ack {
+	/**
+	 * @UM_TIMETRAVEL_START_ACK_ID: client ID that controller allocated.
+	 */
+	UM_TIMETRAVEL_START_ACK_ID = 0xffff,
+};
+
 /**
  * enum um_timetravel_ops - Operation codes
  */
@@ -57,7 +76,9 @@ enum um_timetravel_ops {
 	/**
 	 * @UM_TIMETRAVEL_ACK: response (ACK) to any previous message,
 	 *	this usually doesn't carry any data in the 'time' field
-	 *	unless otherwise specified below
+	 *	unless otherwise specified below, note: while using shared
+	 *	memory no ACK for WAIT and RUN messages, for more info see
+	 *	&struct um_timetravel_schedshm.
 	 */
 	UM_TIMETRAVEL_ACK		= 0,
 
@@ -136,4 +157,134 @@ enum um_timetravel_ops {
 	UM_TIMETRAVEL_BROADCAST		= 9,
 };
 
+/* version of struct um_timetravel_schedshm */
+#define UM_TIMETRAVEL_SCHEDSHM_VERSION 2
+
+/**
+ * enum um_timetravel_schedshm_cap - time travel capabilities of every client
+ *
+ * These flags must be set immediately after processing the ACK to
+ * the START message, before sending any message to the controller.
+ */
+enum um_timetravel_schedshm_cap {
+	/**
+	 * @UM_TIMETRAVEL_SCHEDSHM_CAP_TIME_SHARE: client can read current time
+	 *	update internal time request to shared memory and read
+	 *	free until and send no Ack on RUN and doesn't expect ACK on
+	 *	WAIT.
+	 */
+	UM_TIMETRAVEL_SCHEDSHM_CAP_TIME_SHARE = 0x1,
+};
+
+/**
+ * enum um_timetravel_schedshm_flags - time travel flags of every client
+ */
+enum um_timetravel_schedshm_flags {
+	/**
+	 * @UM_TIMETRAVEL_SCHEDSHM_FLAGS_REQ_RUN: client has a request to run.
+	 *	It's set by client when it has a request to run, if (and only
+	 *	if) the @running_id points to a client that is able to use
+	 *	shared memory, i.e. has %UM_TIMETRAVEL_SCHEDSHM_CAP_TIME_SHARE
+	 *	(this includes the client itself). Otherwise, a message must
+	 *	be used.
+	 */
+	UM_TIMETRAVEL_SCHEDSHM_FLAGS_REQ_RUN = 0x1,
+};
+
+/**
+ * DOC: Time travel shared memory overview
+ *
+ * The main purpose of the shared memory is to avoid all time travel message
+ * that don't need any action, for example current time can be held in shared
+ * memory without the need of any client to send a message UM_TIMETRAVEL_GET
+ * in order to know what's the time.
+ *
+ * Since this is shared memory with all clients and controller and controller
+ * creates the shared memory space, all time values are absolute to controller
+ * time. So first time client connects to shared memory mode it should take the
+ * current_time value in shared memory and keep it internally as a diff to
+ * shared memory times, and once shared memory is initialized, any interaction
+ * with the controller must happen in the controller time domain, including any
+ * messages (for clients that are not using shared memory, the controller will
+ * handle an offset and make the clients think they start at time zero.)
+ *
+ * Along with the shared memory file descriptor is sent to the client a logging
+ * file descriptor, to have all logs related to shared memory,
+ * logged into one place. note: to have all logs synced into log file at write,
+ * file should be flushed (fflush) after writing to it.
+ *
+ * To avoid memory corruption, we define below for each field who can write to
+ * it at what time, defined in the structure fields.
+ *
+ * To avoid having to pack this struct, all fields in it must be naturally aligned
+ * (i.e. aligned to their size).
+ */
+
+/**
+ * union um_timetravel_schedshm_client - UM time travel client struct
+ *
+ * Every entity using the shared memory including the controller has a place in
+ * the um_timetravel_schedshm clients array, that holds info related to the client
+ * using the shared memory, and can be set only by the client after it gets the
+ * fd memory.
+ *
+ * @capa: bit fields with client capabilities see
+ *	&enum um_timetravel_schedshm_cap, set by client once after getting the
+ *	shared memory file descriptor.
+ * @flags: bit fields for flags see &enum um_timetravel_schedshm_flags for doc.
+ * @req_time: request time to run, set by client on every request it needs.
+ * @name: unique id sent to the controller by client with START message.
+ */
+union um_timetravel_schedshm_client {
+	struct {
+		__u32 capa;
+		__u32 flags;
+		__u64 req_time;
+		__u64 name;
+	};
+	char reserve[128]; /* reserved for future usage */
+};
+
+/**
+ * struct um_timetravel_schedshm - UM time travel shared memory struct
+ *
+ * @hdr: header fields:
+ * @version: Current version struct UM_TIMETRAVEL_SCHEDSHM_VERSION,
+ *	set by controller once at init, clients must check this after mapping
+ *	and work without shared memory if they cannot handle the indicated
+ *	version.
+ * @len: Length of all the memory including header (@hdr), clients should once
+ *	per connection first mmap the header and take the length (@len) to remap the entire size.
+ *	This is done in order to support dynamic struct size letting number of
+ *	clients be dynamic based on controller support.
+ * @free_until: Stores the next request to run by any client, in order for the
+ *	current client to know how long it can still run. A client needs to (at
+ *	least) reload this value immediately after communicating with any other
+ *	client, since the controller will update this field when a new request
+ *	is made by any client. Clients also must update this value when they
+ *	insert/update an own request into the shared memory while not running
+ *	themselves, and the new request is before than the current value.
+ * current_time: Current time, can only be set by the client in running state
+ *	(indicated by @running_id), though that client may only run until @free_until,
+ *	so it must remain smaller than @free_until.
+ * @running_id: The current client in state running, set before a client is
+ *	notified that it's now running.
+ * @max_clients: size of @clients array, set once at init by the controller.
+ * @clients: clients array see &union um_timetravel_schedshm_client for doc,
+ *	set only by client.
+ */
+struct um_timetravel_schedshm {
+	union {
+		struct {
+			__u32 version;
+			__u32 len;
+			__u64 free_until;
+			__u64 current_time;
+			__u16 running_id;
+			__u16 max_clients;
+		};
+		char hdr[4096]; /* align to 4K page size */
+	};
+	union um_timetravel_schedshm_client clients[];
+};
 #endif /* _UAPI_LINUX_UM_TIMETRAVEL_H */