Hi everyone,
I'm just submitting to storage lists to see if anyone else thinks
this is useful.
Linux kernel 4.4 adds a new block mode to poll IO for low-latency
storage. When not polling, we can see CPU time spent in system vs. in
iowait. For example, 'mpstat' may show:
CPU %usr %nice %sys %iowait %irq %soft %steal %guest %idle
0 0.00 0.00 40.96 59.04 0.00 0.00 0.00 0.00 0.00
and that's useful to see the iowait, and, when combined with other data,
indicates how the h/w is performing. If we've enabled IO polling, though,
we get something like this:
CPU %usr %nice %sys %iowait %irq %soft %steal %guest %idle
0 0.00 0.00 100.00 0.00 0.00 0.00 0.00 0.00 0.00
Which is pretty useless for gaining insights on how the h/w is
doing. Right now I use 'perf record' to measure where CPU cycles are
spent, but that's not always feasible or convenient.
The following series proposes a new CPU state called "iopoll" so we can
get similarly useful information. The result looks like this:
CPU %usr %nice %sys %iowait %iopoll %irq %soft %steal %guest %gnice %idle
0 1.00 0.00 34.00 0.00 65.00 0.00 0.00 0.00 0.00 0.00 0.00
The first patch is the kernel part. The second is for sysstat. I might
be concerned about the potential for breaking older stats tools...
Thanks!
Keith Busch (1):
CPU: New state for iopoll
block/blk-core.c | 7 ++++++-
fs/proc/stat.c | 8 ++++++--
include/linux/kernel_stat.h | 1 +
include/linux/sched.h | 1 +
kernel/sched/cpuacct.c | 1 +
kernel/sched/cputime.c | 7 ++++++-
6 files changed, 21 insertions(+), 4 deletions(-)
Keith Busch (1):
sysstat: Report iopoll CPU percentage
common.c | 4 ++--
iostat.c | 10 ++++++----
mpstat.c | 18 ++++++++++++------
rd_stats.c | 10 ++++++----
rd_stats.h | 1 +
5 files changed, 27 insertions(+), 16 deletions(-)
--
2.6.2.307.g37023ba
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