Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
04d7b574b2
We already have point-to-multipoint flow control within a group. But we even need the opposite; -a scheme which can handle that potentially hundreds of sources may try to send messages to the same destination simultaneously without causing buffer overflow at the recipient. This commit adds such a mechanism. The algorithm works as follows: - When a member detects a new, joining member, it initially set its state to JOINED and advertises a minimum window to the new member. This window is chosen so that the new member can send exactly one maximum sized message, or several smaller ones, to the recipient before it must stop and wait for an additional advertisement. This minimum window ADV_IDLE is set to 65 1kB blocks. - When a member receives the first data message from a JOINED member, it changes the state of the latter to ACTIVE, and advertises a larger window ADV_ACTIVE = 12 x ADV_IDLE blocks to the sender, so it can continue sending with minimal disturbances to the data flow. - The active members are kept in a dedicated linked list. Each time a message is received from an active member, it will be moved to the tail of that list. This way, we keep a record of which members have been most (tail) and least (head) recently active. - There is a maximum number (16) of permitted simultaneous active senders per receiver. When this limit is reached, the receiver will not advertise anything immediately to a new sender, but instead put it in a PENDING state, and add it to a corresponding queue. At the same time, it will pick the least recently active member, send it an advertisement RECLAIM message, and set this member to state RECLAIMING. - The reclaimee member has to respond with a REMIT message, meaning that it goes back to a send window of ADV_IDLE, and returns its unused advertised blocks beyond that value to the reclaiming member. - When the reclaiming member receives the REMIT message, it unlinks the reclaimee from its active list, resets its state to JOINED, and notes that it is now back at ADV_IDLE advertised blocks to that member. If there are still unread data messages sent out by reclaimee before the REMIT, the member goes into an intermediate state REMITTED, where it stays until the said messages have been consumed. - The returned advertised blocks can now be re-advertised to the pending member, which is now set to state ACTIVE and added to the active member list. - To be proactive, i.e., to minimize the risk that any member will end up in the pending queue, we start reclaiming resources already when the number of active members exceeds 3/4 of the permitted maximum. Signed-off-by: Jon Maloy <jon.maloy@ericsson.com> Acked-by: Ying Xue <ying.xue@windriver.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.