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

[hejianet <hejianet@gmail.com>]

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 
‘cputime_to_nsecs’ [-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(-)
>