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Mohamed Khalfella 1c252d6465 net/mlx5: Added cond_resched() to crdump collection [ Upstream commit `ec79315589` ] Collecting crdump involves reading vsc registers from pci config space of mlx device, which can take long time to complete. This might result in starving other threads waiting to run on the cpu. Numbers I got from testing ConnectX-5 Ex MCX516A-CDAT in the lab: - mlx5_vsc_gw_read_block_fast() was called with length = 1310716. - mlx5_vsc_gw_read_fast() reads 4 bytes at a time. It was not used to read the entire 1310716 bytes. It was called 53813 times because there are jumps in read_addr. - On average mlx5_vsc_gw_read_fast() took 35284.4ns. - In total mlx5_vsc_wait_on_flag() called vsc_read() 54707 times. The average time for each call was 17548.3ns. In some instances vsc_read() was called more than one time when the flag was not set. As expected the thread released the cpu after 16 iterations in mlx5_vsc_wait_on_flag(). - Total time to read crdump was 35284.4ns * 53813 ~= 1.898s. It was seen in the field that crdump can take more than 5 seconds to complete. During that time mlx5_vsc_wait_on_flag() did not release the cpu because it did not complete 16 iterations. It is believed that pci config reads were slow. Adding cond_resched() every 128 register read improves the situation. In the common case the, crdump takes ~1.8989s, the thread yields the cpu every ~4.51ms. If crdump takes ~5s, the thread yields the cpu every ~18.0ms. Fixes: `8b9d8baae1` ("net/mlx5: Add Crdump support") Reviewed-by: Yuanyuan Zhong <yzhong@purestorage.com> Signed-off-by: Mohamed Khalfella <mkhalfella@purestorage.com> Reviewed-by: Moshe Shemesh <moshe@nvidia.com> Signed-off-by: Saeed Mahameed <saeedm@nvidia.com> Signed-off-by: Sasha Levin <sashal@kernel.org>		History 2024-10-10 11:57:14 +02:00
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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.