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c27ea19ea4
trace_sched_blocked_trace in CFS is really useful for debugging via
trace because it tell where the process was stuck on callstack.
For example,
<...>-6143 ( 6136) [005] d..2 50.278987: sched_blocked_reason: pid=6136 iowait=0 caller=SyS_mprotect+0x88/0x208
<...>-6136 ( 6136) [005] d..2 50.278990: sched_blocked_reason: pid=6142 iowait=0 caller=do_page_fault+0x1f4/0x3b0
<...>-6142 ( 6136) [006] d..2 50.278996: sched_blocked_reason: pid=6144 iowait=0 caller=SyS_prctl+0x52c/0xb58
<...>-6144 ( 6136) [006] d..2 50.279007: sched_blocked_reason: pid=6136 iowait=0 caller=vm_mmap_pgoff+0x74/0x104
However, sometime it gives pointless information like this.
RenderThread-2322 ( 1805) [006] d.s3 50.319046: sched_blocked_reason: pid=6136 iowait=1 caller=__lock_page_killable+0x17c/0x220
logd.writer-594 ( 587) [002] d.s3 50.334011: sched_blocked_reason: pid=6126 iowait=1 caller=wait_on_page_bit+0x194/0x208
kworker/u16:13-333 ( 333) [007] d.s4 50.343161: sched_blocked_reason: pid=6136 iowait=1 caller=__lock_page_killable+0x17c/0x220
Such wait_on_page_bit, __lock_page_killable are pointless because it doesn't
carry on higher information to identify the callstack.
The reason is page_lock and waitqueue are special synchronization method unlike
other normal locks(mutex, spinlock).
Let's mark them as "__sched" so get_wchan which used in trace_sched_blocked_trace
could detect it and skip them. It will produce more meaningful callstack
function like this.
<...>-2867 ( 1068) [002] d.h4 124.209701: sched_blocked_reason: pid=329 iowait=0 caller=worker_thread+0x378/0x470
<...>-2867 ( 1068) [002] d.s3 124.209763: sched_blocked_reason: pid=8454 iowait=1 caller=__filemap_fdatawait_range+0xa0/0x104
<...>-2867 ( 1068) [002] d.s4 124.209803: sched_blocked_reason: pid=869 iowait=0 caller=worker_thread+0x378/0x470
ScreenDecoratio-2364 ( 1867) [002] d.s3 124.209973: sched_blocked_reason: pid=8454 iowait=1 caller=f2fs_wait_on_page_writeback+0x84/0xcc
ScreenDecoratio-2364 ( 1867) [002] d.s4 124.209986: sched_blocked_reason: pid=869 iowait=0 caller=worker_thread+0x378/0x470
<...>-329 ( 329) [000] d..3 124.210435: sched_blocked_reason: pid=538 iowait=0 caller=worker_thread+0x378/0x470
kworker/u16:13-538 ( 538) [007] d..3 124.210450: sched_blocked_reason: pid=6 iowait=0 caller=worker_thread+0x378/0x470
Bug: 144961676
Bug: 144713689
Change-Id: I30397400c5d056946bdfbc86c9ef5f4d7e6c98fe
Signed-off-by: Minchan Kim <minchan@google.com>
Signed-off-by: Jimmy Shiu <jimmyshiu@google.com>
Bug: 152417756
(cherry picked from commit 8a780c0eb6800cecbfce21362c2d2a3bcab14e1c)
Signed-off-by: Saravana Kannan <saravanak@google.com>
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.