Deferred IO is a way to delay and repurpose IO. It uses host memory as a
buffer and the MMU pagefault as a pretrigger for when to perform the device
-IO. The following example may be a useful explaination of how one such setup
+IO. The following example may be a useful explanation of how one such setup
works:
- userspace app like Xfbdev mmaps framebuffer
-- deferred IO and driver sets up nopage and page_mkwrite handlers
+- deferred IO and driver sets up fault and page_mkwrite handlers
- userspace app tries to write to mmaped vaddress
-- we get pagefault and reach nopage handler
-- nopage handler finds and returns physical page
+- we get pagefault and reach fault handler
+- fault handler finds and returns physical page
- we get page_mkwrite where we add this page to a list
- schedule a workqueue task to be run after a delay
- app continues writing to that page with no additional cost. this is
For some types of nonvolatile high latency displays, the desired image is
the final image rather than the intermediate stages which is why it's okay
-to not update for each write that is occuring.
+to not update for each write that is occurring.
It may be the case that this is useful in other scenarios as well. Paul Mundt
has mentioned a case where it is beneficial to use the page count to decide
projects / cascardo / linux.git / blobdiff