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Whenever we notice some sluggish issues on our machines, we are always curious about how well all types of I/O in the f2fs filesystem are handled. But, it's hard to get this kind of real data. First of all, we need to reproduce the issue while turning on the profiling tool like blktrace, but the issue doesn't happen again easily. Second, with the intervention of any tools, the overall timing of the issue will be slightly changed and it sometimes makes us hard to figure it out. So, I added the feature printing out IO latency statistics tracepoint events, which are minimal things to understand filesystem's I/O related behaviors, into F2FS_IOSTAT kernel config. With "iostat_enable" sysfs node on, we can get this statistics info in a periodic way and it would cause the least overhead. [samples] f2fs_ckpt-254:1-507 [003] .... 2842.439683: f2fs_iostat_latency: dev = (254,11), iotype [peak lat.(ms)/avg lat.(ms)/count], rd_data [136/1/801], rd_node [136/1/1704], rd_meta [4/2/4], wr_sync_data [164/16/3331], wr_sync_node [152/3/648], wr_sync_meta [160/2/4243], wr_async_data [24/13/15], wr_async_node [0/0/0], wr_async_meta [0/0/0] f2fs_ckpt-254:1-507 [002] .... 2845.450514: f2fs_iostat_latency: dev = (254,11), iotype [peak lat.(ms)/avg lat.(ms)/count], rd_data [60/3/456], rd_node [60/3/1258], rd_meta [0/0/1], wr_sync_data [120/12/2285], wr_sync_node [88/5/428], wr_sync_meta [52/6/2990], wr_async_data [4/1/3], wr_async_node [0/0/0], wr_async_meta [0/0/0] Signed-off-by: Daeho Jeong <daehojeong@google.com> Reviewed-by: Chao Yu <chao@kernel.org> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
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.