Re: [GIT PULL] cputime: Convert core use of cputime_t to nsecs

From: hejianet
Date: Tue Feb 21 2017 - 00:08:54 EST

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Hi Frederic

Do we need to support CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=n on ppc64le?

If yes, I got a compiling error after applying your patch set:

arch/powerpc/kernel/time.c:712:2: error: implicit declaration of function ‚Äòcputime_to_nsecs‚Äô [-Werror=implicit-function-declaration]
return local_clock() - cputime_to_nsecs(kcpustat_this_cpu->cpustat[CPUTIME_STEAL]);
^

I thought it is due to CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=n on my ppc64le server.
My kernel config:
# grep -n CONFIG_VIRT_CPU .config
136:CONFIG_VIRT_CPU_ACCOUNTING=y
137:CONFIG_VIRT_CPU_ACCOUNTING_GEN=y

B.R.
Jia

On 30/01/2017 12:46 PM, Frederic Weisbecker wrote:

Ingo,

Please pull the cputime/nsecs-for-tip branch that can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
cputime/nsecs-for-tip

HEAD: 14d889bef71ff808c450f82bcd257b10f05bb061

The patches are the same than on my previous post: https://lwn.net/Articles/712213/
If you apply them by email, just please ignore the very last one
([PATCH 37/37] s390: Prevent from cputime leaks) because we need to find
a better solution with Martin. The branch doesn't have this patch.

--- Summary ---

cputime_t is a type that can map to different time units and
granularities: jiffies, nsecs or architecture clock.

This type and its accessors and mutators have been designed to deal
with all these time units that can vary depending on the kernel config
in order to support a model where the cputime is stored as-is under
the source unit.

The pro here with this model is to avoid expensive conversions from the
source unit cputime to a more generic type during the accounting hotpath.
Especially for config that have CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y.

Now there are several cons:

* we need to maintain a whole set of cputime_t mutators and accessors
for all implementations of cputime_t (currently 4 of them). And we
need such function for every kind of time conversion: to/from
jiffies, nsecs, usecs, timeval, clock_t, ...

* The core code needs to deal with different possible granularities
of cputime_t while converting to/from another time unit.
Especially functions like nsecs_to_cputime() can leak some nsecs
remainder. This adds more complexity and even sometimes performance
loss (involving reverse conversion) in order to avoid losing such
time remainder (eg: irqtime accounting, steal time accounting, posix
cpu timers, ...).

* Kernel developers are seldom familiar with these granularity issues:
cputime leaks often appear in patches dealing with cputime code.

* In general cputime_t, as a varying type, is more opaque and harder
to deal with than static nsecs. Making the core code less readable.

This patchset removes all core use of cputime_t and stores the cputime
into nsecs units. Only s390 and powerpc
(with CONFIG_VIRT_CPU_ACCOUNTING_NATIVE for the latter) now still use
cputime_t.

Many code get simplified, the diffstat is appealing and some fastpath
should even have a small performance gain (irqtime and steal time
accounting).

Now lets admit one drawback: s390 and powerpc with
CONFIG_VIRT_CPU_ACCOUNTING_NATIVE have new cputime_t to nsecs conversion
on cputime accounting path. But this should be leveraged by the recent
changes which delay the cputime accounting to tick and context switch.

Thanks,
Frederic
---

Frederic Weisbecker (36):
jiffies: Reuse TICK_NSEC instead of NSEC_PER_JIFFY
time: Introduce jiffies64_to_nsecs()
sched: Remove unused INIT_CPUTIME macro
cputime: Convert kcpustat to nsecs
macintosh/rack-meter: Remove cputime_t internal use
cputime: Convert guest time accounting to nsecs
cputime: Special API to return old-typed cputime
cputime: Convert task/group cputime to nsecs
alpha: Convert obsolete cputime_t to nsecs
x86: Convert obsolete cputime type to nsecs
isdn: Convert obsolete cputime type to nsecs
binfmt: Convert obsolete cputime type to nsecs
acct: Convert obsolete cputime type to nsecs
delaycct: Convert obsolete cputime type to nsecs
tsacct: Convert obsolete cputime type to nsecs
signal: Convert obsolete cputime type to nsecs
cputime: Increment kcpustat directly on irqtime account
posix-timers: Use TICK_NSEC instead of a dynamically ad-hoc calculated version
posix-timers: Convert internals to use nsecs
itimer: Convert internal cputime_t units to nsec
sched: Remove temporary cputime_t accessors
cputime: Push time to account_user_time() in nsecs
cputime: Push time to account_steal_time() in nsecs
cputime: Push time to account_idle_time() in nsecs
cputime: Push time to account_system_time() in nsecs
cputime: Complete nsec conversion of tick based accounting
vtime: Return nsecs instead of cputime_t to account
cputime: Remove jiffies based cputime
ia64: Move nsecs based cputime headers to the last arch using it
ia64: Convert vtime to use nsec units directly
ia64: Remove unused cputime definitions
s390: Make arch_cpu_idle_time() to return nsecs
powerpc: Remove unused cputime definitions
s390: Remove unused cputime definitions
cputime: Remove unused nsec_to_cputime
cputime: Remove asm generic headers

arch/alpha/include/asm/Kbuild | 1 -
arch/alpha/kernel/osf_sys.c | 10 +-
arch/arc/include/asm/Kbuild | 1 -
arch/arm/include/asm/Kbuild | 1 -
arch/arm64/include/asm/Kbuild | 1 -
arch/avr32/include/asm/Kbuild | 1 -
arch/blackfin/include/asm/Kbuild | 1 -
arch/c6x/include/asm/Kbuild | 1 -
arch/cris/include/asm/Kbuild | 1 -
arch/frv/include/asm/Kbuild | 1 -
arch/h8300/include/asm/Kbuild | 1 -
arch/hexagon/include/asm/Kbuild | 1 -
arch/ia64/include/asm/cputime.h | 6 +-
arch/ia64/kernel/head.S | 4 +-
arch/ia64/kernel/time.c | 17 ++--
arch/m32r/include/asm/Kbuild | 1 -
arch/m68k/include/asm/Kbuild | 1 -
arch/metag/include/asm/Kbuild | 1 -
arch/microblaze/include/asm/Kbuild | 1 -
arch/mips/include/asm/Kbuild | 1 -
arch/mips/kernel/binfmt_elfn32.c | 12 +--
arch/mips/kernel/binfmt_elfo32.c | 12 +--
arch/mn10300/include/asm/Kbuild | 1 -
arch/nios2/include/asm/Kbuild | 1 -
arch/openrisc/include/asm/Kbuild | 1 -
arch/parisc/include/asm/Kbuild | 1 -
arch/parisc/kernel/binfmt_elf32.c | 11 +--
arch/powerpc/include/asm/cputime.h | 177 +---------------------------------
arch/powerpc/kernel/time.c | 45 +++------
arch/s390/appldata/appldata_os.c | 16 +--
arch/s390/include/asm/cputime.h | 109 +--------------------
arch/s390/kernel/idle.c | 9 +-
arch/s390/kernel/vtime.c | 16 +--
arch/score/include/asm/Kbuild | 1 -
arch/sh/include/asm/Kbuild | 1 -
arch/sparc/include/asm/Kbuild | 1 -
arch/tile/include/asm/Kbuild | 1 -
arch/um/include/asm/Kbuild | 1 -
arch/unicore32/include/asm/Kbuild | 1 -
arch/x86/include/asm/Kbuild | 1 -
arch/x86/kernel/apm_32.c | 6 +-
arch/x86/kvm/hyperv.c | 5 +-
arch/xtensa/include/asm/Kbuild | 1 -
drivers/cpufreq/cpufreq.c | 6 +-
drivers/cpufreq/cpufreq_governor.c | 2 +-
drivers/cpufreq/cpufreq_stats.c | 1 -
drivers/isdn/mISDN/stack.c | 4 +-
drivers/macintosh/rack-meter.c | 28 +++---
fs/binfmt_elf.c | 15 +--
fs/binfmt_elf_fdpic.c | 14 +--
fs/compat_binfmt_elf.c | 18 +---
fs/proc/array.c | 16 +--
fs/proc/stat.c | 64 ++++++------
fs/proc/uptime.c | 7 +-
include/asm-generic/cputime.h | 15 ---
include/asm-generic/cputime_jiffies.h | 75 --------------
include/asm-generic/cputime_nsecs.h | 121 -----------------------
include/linux/compat.h | 20 +++-
include/linux/cputime.h | 7 +-
include/linux/jiffies.h | 2 +
include/linux/kernel_stat.h | 13 ++-
include/linux/posix-timers.h | 14 +--
include/linux/sched.h | 62 +++++-------
include/trace/events/timer.h | 26 ++---
kernel/acct.c | 7 +-
kernel/delayacct.c | 6 +-
kernel/exit.c | 4 +-
kernel/fork.c | 2 +-
kernel/sched/cpuacct.c | 2 +-
kernel/sched/cputime.c | 166 +++++++++++++------------------
kernel/sched/sched.h | 7 +-
kernel/sched/stats.h | 4 +-
kernel/signal.c | 12 +--
kernel/sys.c | 16 +--
kernel/time/itimer.c | 60 ++++--------
kernel/time/jiffies.c | 32 +++---
kernel/time/posix-cpu-timers.c | 170 ++++++++++++--------------------
kernel/time/time.c | 10 ++
kernel/time/timeconst.bc | 6 ++
kernel/tsacct.c | 21 ++--
80 files changed, 436 insertions(+), 1102 deletions(-)

Next message: Service Loans: "Fast Loans"
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Next in thread: Frederic Weisbecker: "Re: [GIT PULL] cputime: Convert core use of cputime_t to nsecs"
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