starfive-tech/linux.git - StarFive Tech Linux Kernel for VisionFive (JH7110) boards (mirror)

Age	Commit message (Collapse)	Author	Files	Lines
2017-07-14	percpu-rw-semaphore.txt: standardize document format	Mauro Carvalho Chehab	1	-1/+2
	Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: This document is already adopting the standard format, with a single exception: we're using this convention for the document title: === foo === So, adjust the title of this document to follow the standard. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2012-09-26	percpu-rw-semaphore: fix documentation typos	Mikulas Patocka	1	-2/+2
	One more patch for this thing, fixing some typos in the documentation. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
2012-09-26	blockdev: turn a rw semaphore into a percpu rw semaphore	Mikulas Patocka	1	-0/+27
	This avoids cache line bouncing when many processes lock the semaphore for read. New percpu lock implementation The lock consists of an array of percpu unsigned integers, a boolean variable and a mutex. When we take the lock for read, we enter rcu read section, check for a "locked" variable. If it is false, we increase a percpu counter on the current cpu and exit the rcu section. If "locked" is true, we exit the rcu section, take the mutex and drop it (this waits until a writer finished) and retry. Unlocking for read just decreases percpu variable. Note that we can unlock on a difference cpu than where we locked, in this case the counter underflows. The sum of all percpu counters represents the number of processes that hold the lock for read. When we need to lock for write, we take the mutex, set "locked" variable to true and synchronize rcu. Since RCU has been synchronized, no processes can create new read locks. We wait until the sum of percpu counters is zero - when it is, there are no readers in the critical section. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>