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The linux-next integration testing tree
33391eecd6
We ran into an issue where a production workload would randomly grind to a halt and not continue until the pending IO had timed out. This turned out to be a complicated interaction between queue freezing and polled IO: 1) You have an application that does polled IO. At any point in time, there may be polled IO pending. 2) You have a monitoring application that issues a passthrough command, which is marked with side effects such that it needs to freeze the queue. 3) Passthrough command is started, which calls blk_freeze_queue_start() on the device. At this point the queue is marked frozen, and any attempt to enter the queue will fail (for non-blocking) or block. 4) Now the driver calls blk_mq_freeze_queue_wait(), which will return when the queue is quiesced and pending IO has completed. 5) The pending IO is polled IO, but any attempt to poll IO through the normal iocb_bio_iopoll() -> bio_poll() will fail when it gets to bio_queue_enter() as the queue is frozen. Rather than poll and complete IO, the polling threads will sit in a tight loop attempting to poll, but failing to enter the queue to do so. The end result is that progress for either application will be stalled until all pending polled IO has timed out. This causes obvious huge latency issues for the application doing polled IO, but also long delays for passthrough command. Fix this by treating queue enter for polled IO just like we do for timeouts. This allows quick quiesce of the queue as we still poll and complete this IO, while still disallowing queueing up new IO. Reviewed-by: Keith Busch <kbusch@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
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| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
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| README | ||
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.