3ec4848913
While monitoring the throttle time of IO from iocost, it's found that
such time is always zero after the io_schedule() from ioc_rqos_throttle,
for example, with the following debug patch:
+ printk("%s-%d: %s enter %llu\n", current->comm, current->pid, __func__, blk_time_get_ns());
while (true) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (wait.committed)
break;
io_schedule();
}
+ printk("%s-%d: %s exit %llu\n", current->comm, current->pid, __func__, blk_time_get_ns());
It can be observerd that blk_time_get_ns() always return the same time:
[ 1068.096579] fio-1268: ioc_rqos_throttle enter 1067901962288
[ 1068.272587] fio-1268: ioc_rqos_throttle exit 1067901962288
[ 1068.274389] fio-1268: ioc_rqos_throttle enter 1067901962288
[ 1068.472690] fio-1268: ioc_rqos_throttle exit 1067901962288
[ 1068.474485] fio-1268: ioc_rqos_throttle enter 1067901962288
[ 1068.672656] fio-1268: ioc_rqos_throttle exit 1067901962288
[ 1068.674451] fio-1268: ioc_rqos_throttle enter 1067901962288
[ 1068.872655] fio-1268: ioc_rqos_throttle exit 1067901962288
And I think the root cause is that 'PF_BLOCK_TS' is always cleared
by blk_flush_plug() before scheduel(), hence blk_plug_invalidate_ts()
will never be called:
blk_time_get_ns
plug->cur_ktime = ktime_get_ns();
current->flags |= PF_BLOCK_TS;
io_schedule:
io_schedule_prepare
blk_flush_plug
__blk_flush_plug
/* the flag is cleared, while time is not */
current->flags &= ~PF_BLOCK_TS;
schedule
sched_update_worker
/* the flag is not set, hence plug->cur_ktime is not cleared */
if (tsk->flags & PF_BLOCK_TS)
blk_plug_invalidate_ts()
blk_time_get_ns
/* got the time stashed before schedule */
return plug->cur_ktime;
Fix the problem by clearing cached time in __blk_flush_plug().
Fixes:
|
||
---|---|---|
Documentation | ||
LICENSES | ||
arch | ||
block | ||
certs | ||
crypto | ||
drivers | ||
fs | ||
include | ||
init | ||
io_uring | ||
ipc | ||
kernel | ||
lib | ||
mm | ||
net | ||
rust | ||
samples | ||
scripts | ||
security | ||
sound | ||
tools | ||
usr | ||
virt | ||
.clang-format | ||
.cocciconfig | ||
.editorconfig | ||
.get_maintainer.ignore | ||
.gitattributes | ||
.gitignore | ||
.mailmap | ||
.rustfmt.toml | ||
COPYING | ||
CREDITS | ||
Kbuild | ||
Kconfig | ||
MAINTAINERS | ||
Makefile | ||
README |
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 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.