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Darrick J. Wong 271557de7c xfs: reduce the rate of cond_resched calls inside scrub
We really don't want to call cond_resched every single time we go
through a loop in scrub -- there may be billions of records, and probing
into the scheduler itself has overhead.  Reduce this overhead by only
calling cond_resched 10x per second; and add a counter so that we only
check jiffies once every 1000 records or so.

Surprisingly, this reduces scrub-only fstests runtime by about 2%.  I
used the bmapinflate xfs_db command to produce a billion-extent file and
this stupid gadget reduced the scrub runtime by about 4%.

From a stupid microbenchmark of calling these things 1 billion times, I
estimate that cond_resched costs about 5.5ns per call; jiffes costs
about 0.3ns per read; and fatal_signal_pending costs about 0.4ns per
call.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
History 2024-04-23 16:55:17 -07:00
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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 reStructuredText 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.