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0ba93a906d
Try to handle loop aio command via NOWAIT IO first, then we can avoid to queue the aio command into workqueue. This is usually one big win in case that FS block mapping is stable, Mikulas verified [1] that this way improves IO perf by close to 5X in 12jobs sequential read/write test, in which FS block mapping is just stable. Fallback to workqueue in case of -EAGAIN. This way may bring a little cost from the 1st retry, but when running the following write test over loop/sparse_file, the actual effect on randwrite is obvious: ``` truncate -s 4G 1.img #1.img is created on XFS/virtio-scsi losetup -f 1.img --direct-io=on fio --direct=1 --bs=4k --runtime=40 --time_based --numjobs=1 --ioengine=libaio \ --iodepth=16 --group_reporting=1 --filename=/dev/loop0 -name=job --rw=$RW ``` - RW=randwrite: obvious IOPS drop observed - RW=write: a little drop(%5 - 10%) This perf drop on randwrite over sparse file will be addressed in the following patch. BLK_MQ_F_BLOCKING has to be set for calling into .read_iter() or .write_iter() which might sleep even though it is NOWAIT, and the only effect is that rcu read lock is replaced with srcu read lock. Link: https://lore.kernel.org/linux-block/a8e5c76a-231f-07d1-a394-847de930f638@redhat.com/ [1] Signed-off-by: Ming Lei <ming.lei@redhat.com> 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 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.