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0006707723
Doing high IOPS testing with blk-cgroups enabled spends ~15-20% of the time just doing ktime_get_ns() -> readtsc. We essentially read and set the start time twice, one for the bio and then again when that bio is mapped to a request. Given that the time between the two is very short, inherit the bio start time instead of reading it again. This cuts 1/3rd of the overhead of the time keeping. Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.