Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
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'struct frame' uses two variables to store the sent timestamp - 'struct timeval' and jiffies. jiffies is used to avoid discrepancies caused by updates to system time. 'struct timeval' is deprecated because it uses 32-bit representation for seconds which will overflow in year 2038. This patch does the following: - Replace the use of 'struct timeval' and jiffies with ktime_t, which is the recommended type for timestamping - ktime_t provides both long range (like jiffies) and high resolution (like timeval). Using ktime_get (monotonic time) instead of wall-clock time prevents any discprepancies caused by updates to system time. [updates by Arnd below] The original patch from Tina never went anywhere as we discussed how to keep the impact on performance minimal. I've started over now but arrived at basically the same patch that she had originally, except for an slightly improved tsince_hr() function. I'm making it more robust against overflows, and also optimize explicitly for the common case in which a frame is less than 4.2 seconds old, using only a 32-bit division in that case. This should make the new version more efficient than the old code, since we replace the existing two 32-bit division in do_gettimeofday() plus one multiplication with a single single 32-bit division in tsince_hr() and drop the double bookkeeping. It's also more efficient than the ktime_get_us() API we discussed before, since that would also rely on multiple divisions. Link: https://lists.linaro.org/pipermail/y2038/2015-May/000276.html Signed-off-by: Tina Ruchandani <ruchandani.tina@gmail.com> Cc: Ed Cashin <ed.cashin@acm.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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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.